arm: Use little endian packet accessors.

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

Change-Id: Iee337109fcda134e1ac5a700e5141fd7060f9c45
Reviewed-on: https://gem5-review.googlesource.com/c/13457
Reviewed-by: Andreas Sandberg <andreas.sandberg@arm.com>
Maintainer: Andreas Sandberg <andreas.sandberg@arm.com>

dev-arm: Factory SimObject for generating ArmInterruptPin

With this patch the python ArmInterruptPin SimObject matches to the
C++ ArmInterruptPinGen. The latter is in charge of generating
the ArmInterruptPin (which is not a SimObject anymore).
This is meant to ease the generation of ArmInterruptPins: by
not being SimObjects we are not forced to instantiate them
in the configuration script; we can generate them dynamically
instead throughout simulation.

Change-Id: I917d73a26168447221f5993c8ae975ee3771e3bf
Signed-off-by: Giacomo Travaglini <giacomo.travaglini@arm.com>
Reviewed-by: Andreas Sandberg <andreas.sandberg@arm.com>
Reviewed-on: https://gem5-review.googlesource.com/12401
Maintainer: Andreas Sandberg <andreas.sandberg@arm.com>

dev-arm: Add a MMIO transport interface for VirtIO

The MMIO interface currently only supports a subset of version 0.9.5
of the VirtIO specification. It has the following known limitations:

* The queue size hint (the QUEUE_NUM register) is ignored.

* Queue alignment is assumed to be hard-coded to
VirtQueue::ALIGN_SIZE (4096 bytes).

* Only 4096 byte pages are currently supported.

Change-Id: Ifd318f5e5bddab0b6a42d8c8af9ff2fbb477f98b
Signed-off-by: Andreas Sandberg <andreas.sandberg@arm.com>
Reviewed-by: Nikos Nikoleris <nikos.nikoleris@arm.com>
Reviewed-by: Rekai Gonzalez Alberquilla <rekai.gonzalezalberquilla@arm.com>
Reviewed-on: https://gem5-review.googlesource.com/2326
Reviewed-by: Giacomo Travaglini <giacomo.travaglini@arm.com>