ArmVirtualizationPkg/PciHostBridgeDxe: MMIO aperture must not be uncached

ArmVirtualizationPkg/PciHostBridgeDxe: MMIO aperture must not be uncached

Quite non-intuitively, we must allow guest-side writes to emulated PCI
MMIO regions to go through the CPU cache, otherwise QEMU, whose accesses
always go through the cache, may see stale data in the region.

This change makes no difference for QEMU/TCG, but it is important for
QEMU/KVM, at the moment.

Because gDS->SetMemorySpaceAttributes() is ultimately implemented by
EFI_CPU_ARCH_PROTOCOL.SetMemoryAttributes() -- see
"MdeModulePkg/Core/Dxe/Gcd/Gcd.c" and "ArmPkg/Drivers/CpuDxe/" -- we add
the CPU architectural protocol to the module's DepEx.

Contributed-under: TianoCore Contribution Agreement 1.0
Signed-off-by: Laszlo Ersek <lersek@redhat.com>
Reviewed-by: Ard Biesheuvel <ard.biesheuvel@linaro.org>
Reviewed-by: Olivier Martin <olivier.martin@arm.com>
git-svn-id: https://svn.code.sf.net/p/edk2/code/trunk/edk2@16904 6f19259b-4bc3-4df7-8a09-765794883524