ArmVirtualizationPkg: add a relocatable version of PrePi

ArmVirtualizationPkg: add a relocatable version of PrePi

This patch introduces a relocatable PrePi, which can execute
from arbitrary offsets in RAM. This is intendend to be run
from a boot loader which passes a description of the actual
platform in a device tree, for instance.

This module is based on the PrePi implementations residing under
ArmPlatformPkg.

Contributed-under: TianoCore Contribution Agreement 1.0
Reviewed-by: Olivier Martin <olivier.martin@arm.com>
Signed-off-by: Ard Biesheuvel <ard.biesheuvel@linaro.org>
Signed-off-by: Laszlo Ersek <lersek@redhat.com>
git-svn-id: https://svn.code.sf.net/p/edk2/code/trunk/edk2@16961 6f19259b-4bc3-4df7-8a09-765794883524