x86: Use little endian packet accessors.

We know data is little endian, so we can use those accessors
explicitly.

Change-Id: I09aa7f1e525ad1346e932ce4a772b64bf59dc350
Reviewed-on: https://gem5-review.googlesource.com/c/13456
Reviewed-by: Andreas Sandberg <andreas.sandberg@arm.com>
Maintainer: Gabe Black <gabeblack@google.com>

base: Rework bitunions so they can be more flexible.

They are now oriented around a class which makes it easy to provide
custom setter/getter functions which let you set or read bits in an
arbitrary way.

Future additions may add the ability to add custom bitfield methods,
and index-able bitfields.

Change-Id: Ibd6d4d9e49107490f6dad30a4379a8c93bda9333
Reviewed-on: https://gem5-review.googlesource.com/7201
Reviewed-by: Jason Lowe-Power <jason@lowepower.com>
Maintainer: Gabe Black <gabeblack@google.com>

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

sim: Refactor the serialization base class

Objects that are can be serialized are supposed to inherit from the
Serializable class. This class is meant to provide a unified API for
such objects. However, so far it has mainly been used by SimObjects
due to some fundamental design limitations. This changeset redesigns
to the serialization interface to make it more generic and hide the
underlying checkpoint storage. Specifically:

* Add a set of APIs to serialize into a subsection of the current
object. Previously, objects that needed this functionality would
use ad-hoc solutions using nameOut() and section name
generation. In the new world, an object that implements the
interface has the methods serializeSection() and
unserializeSection() that serialize into a named /subsection/ of
the current object. Calling serialize() serializes an object into
the current section.

* Move the name() method from Serializable to SimObject as it is no
longer needed for serialization. The fully qualified section name
is generated by the main serialization code on the fly as objects
serialize sub-objects.

* Add a scoped ScopedCheckpointSection helper class. Some objects
need to serialize data structures, that are not deriving from
Serializable, into subsections. Previously, this was done using
nameOut() and manual section name generation. To simplify this,
this changeset introduces a ScopedCheckpointSection() helper
class. When this class is instantiated, it adds a new /subsection/
and subsequent serialization calls during the lifetime of this
helper class happen inside this section (or a subsection in case
of nested sections).

* The serialize() call is now const which prevents accidental state
manipulation during serialization. Objects that rely on modifying
state can use the serializeOld() call instead. The default
implementation simply calls serialize(). Note: The old-style calls
need to be explicitly called using the
serializeOld()/serializeSectionOld() style APIs. These are used by
default when serializing SimObjects.

* Both the input and output checkpoints now use their own named
types. This hides underlying checkpoint implementation from
objects that need checkpointing and makes it easier to change the
underlying checkpoint storage code.

trace: reimplement the DTRACE function so it doesn't use a vector
At the same time, rename the trace flags to debug flags since they
have broader usage than simply tracing. This means that
--trace-flags is now --debug-flags and --trace-help is now --debug-help

x86: Add checkpointing capability to devices

Add checkpointing capability to the Intel 8254 timer, CMOS, I8042,
PS2 Keyboard and Mouse, I82094AA, I8237, I8254, I8259, and speaker
devices

X86: Add makeAtomicResponse to the read/write functions of x86 devices.

X86: Change I8254 and PCSpeaker devices from subdevices to SimObjects and eliminate subdevices.