arch, base, sim: Demote (SE|FS)TranslatingPortProxy &s to PortProxy &s.

Al(most) all of the interesting differences between the two classes
have been removed. There are some control methods which are still
specific to each type which may require treating them as their true
type, but most code that consumes them doesn't need to worry about
which is which.

Change-Id: Ie592676f1e496c7940605b66e55cd7fae18e59d6
Reviewed-on: https://gem5-review.googlesource.com/c/public/gem5/+/18577
Tested-by: kokoro <noreply+kokoro@google.com>
Reviewed-by: Jason Lowe-Power <jason@lowepower.com>
Reviewed-by: Brandon Potter <Brandon.Potter@amd.com>
Reviewed-by: Andreas Sandberg <andreas.sandberg@arm.com>
Maintainer: Andreas Sandberg <andreas.sandberg@arm.com>

arch, base, sim: Replace Copy(String)?(In|Out) with equivalent code.

This expands those functions into code which extracts the virt proxy
and then uses the appropriate method on it. This has two benefits.
First, the Copy* functions where mostly redundant wrappers around the
methods the proxy port already had. Second, using them forced a
particular port which might not actually be what the user wanted.

Change-Id: I62084631dd080061e3c74997125164f40da2d77c
Reviewed-on: https://gem5-review.googlesource.com/c/public/gem5/+/18575
Reviewed-by: Jason Lowe-Power <jason@lowepower.com>
Maintainer: Jason Lowe-Power <jason@lowepower.com>
Tested-by: kokoro <noreply+kokoro@google.com>

mem: Remove the ISA specialized versions of port proxy's read/write.

These selected their behavior based on ifdefs and had to be disabled
when on the NULL ISA. The versions which take an explicit endianness
have been renamed to just read/write instead of readGtoH and writeHtoG
since the direction of the translation is obvious from context.

Change-Id: I6cfbfda6c4481962d442d3370534e50532d41814
Reviewed-on: https://gem5-review.googlesource.com/c/public/gem5/+/18372
Reviewed-by: Gabe Black <gabeblack@google.com>
Maintainer: Gabe Black <gabeblack@google.com>
Tested-by: kokoro <noreply+kokoro@google.com>

style: [patch 1/22] use /r/3648/ to reorganize includes

arch: Use const StaticInstPtr references where possible

This patch optimises the passing of StaticInstPtr by avoiding copying
the reference-counting pointer. This avoids first incrementing and
then decrementing the reference-counting pointer.

MEM: Make port proxies use references rather than pointers

This patch is adding a clearer design intent to all objects that would
not be complete without a port proxy by making the proxies members
rathen than dynamically allocated. In essence, if NULL would not be a
valid value for the proxy, then we avoid using a pointer to make this
clear.

The same approach is used for the methods using these proxies, such as
loadSections, that now use references rather than pointers to better
reflect the fact that NULL would not be an acceptable value (in fact
the code would break and that is how this patch started out).

Overall the concept of "using a reference to express unconditional
composition where a NULL pointer is never valid" could be done on a
much broader scale throughout the code base, but for now it is only
done in the locations affected by the proxies.

Merge with the main repo.

SE/FS: Get rid of FULL_SYSTEM in MIPS.

MEM: Add port proxies instead of non-structural ports

Port proxies are used to replace non-structural ports, and thus enable
all ports in the system to correspond to a structural entity. This has
the advantage of accessing memory through the normal memory subsystem
and thus allowing any constellation of distributed memories, address
maps, etc. Most accesses are done through the "system port" that is
used for loading binaries, debugging etc. For the entities that belong
to the CPU, e.g. threads and thread contexts, they wrap the CPU data
port in a port proxy.

The following replacements are made:
FunctionalPort > PortProxy
TranslatingPort > SETranslatingPortProxy
VirtualPort > FSTranslatingPortProxy

MIPS: Many style fixes.
White space, commented out code, some other minor fixes.

arch: TheISA shouldn't really ever be used in the arch directory.
We should always refer to the specific ISA in that arch directory.
This is especially necessary if we're ever going to make it to the
point where we actually have heterogeneous systems.

Remove delVirtPort() and make getVirtPort() only return cached version.

fix MIPS headers

Add in files from merge-bare-iron, get them compiling in FS and SE mode