mem: Minimize the use of MemObject.

MemObject doesn't provide anything beyond its base ClockedObject any
more, so this change removes it from most inheritance hierarchies.
Occasionally MemObject is replaced with SimObject when I was fairly
confident that the extra functionality of ClockedObject wasn't needed.

Change-Id: Ic014ab61e56402e62548e8c831eb16e26523fdce
Reviewed-on: https://gem5-review.googlesource.com/c/public/gem5/+/18289
Tested-by: kokoro <noreply+kokoro@google.com>
Reviewed-by: Anthony Gutierrez <anthony.gutierrez@amd.com>
Maintainer: Gabe Black <gabeblack@google.com>

arch, cpu, dev, gpu, mem, sim, python: start using getPort.

Replace the getMasterPort, getSlavePort, and getEthPort functions
with getPort, and remove extraneous mechanisms that are no longer
necessary.

Change-Id: Iab7e3c02d2f3a0cf33e7e824e18c28646b5bc318
Reviewed-on: https://gem5-review.googlesource.com/c/public/gem5/+/17040
Reviewed-by: Daniel Carvalho <odanrc@yahoo.com.br>
Reviewed-by: Andreas Sandberg <andreas.sandberg@arm.com>
Maintainer: Andreas Sandberg <andreas.sandberg@arm.com>

sim,cpu,mem,arch: Introduced MasterInfo data structure

With this patch a gem5 System will store more info about its Masters.
While it was previously keeping track of the Master name and Master ID
only, it is now adding a per-Master pointer to the SimObject related to
the Master.
This will make it possible for a client to query a System for a Master
using either the master's name or the master's pointer.

Change-Id: I8b97d328a65cd06f329e2cdd3679451c17d2b8f6
Signed-off-by: Giacomo Travaglini <giacomo.travaglini@arm.com>
Reviewed-by: Andreas Sandberg <andreas.sandberg@arm.com>
Reviewed-on: https://gem5-review.googlesource.com/9781
Reviewed-by: Jason Lowe-Power <jason@lowepower.com>
Maintainer: Nikos Nikoleris <nikos.nikoleris@arm.com>

misc: add a MasterId to the ExternalPort

The Request constructor requires a MasterID. However, an external
transactor has no chance of getting a MasterID as it does not have a
pointer to the System. This patch adds a MasterID to ExternalMaster to
allow external modules to easily genrerate new Requests.

Signed-off-by: Jason Lowe-Power <jason@lowepower.com>

style: [patch 3/22] reduce include dependencies in some headers

Used cppclean to help identify useless includes and removed them. This
involved erroneously included headers, but also cases where forward
declarations could have been used rather than a full include.

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

mem: Add ExternalMaster and ExternalSlave ports

This patch adds two MemoryObject's: ExternalMaster and ExternalSlave.
Each object has a single port which can be bound to an externally-
provided bridge to a port of another simulation system at
initialisation.