ArmVirtualizationPkg: Xen: shuffle init order to deal with incoherency

ArmVirtualizationPkg: Xen: shuffle init order to deal with incoherency

In order to prevent memory corruption issues caused by the fact that,
under virtualization, the guest is incoherent with the hypervisor's view
of memory until it enables its caches and MMU, this patch reshuffles the
init sequence so that the Xen shared memory regions are not touched
before the caches and MMU are enabled.

In addition, the loaded image itself is invalidated by virtual address,
to ensure that any runtime changes (such as the applied relocations) will
not suddenly become invisible once we turn the caches on.

Contributed-under: TianoCore Contribution Agreement 1.0
Reviewed-by: Olivier Martin <Olivier.Martin@arm.com>
Signed-off-by: Ard Biesheuvel <ard.biesheuvel@linaro.org>
git-svn-id: https://svn.code.sf.net/p/edk2/code/trunk/edk2@17178 6f19259b-4bc3-4df7-8a09-765794883524