ArmVExpressPkg: use PSCI for system reset at runtime

ArmVExpressPkg: use PSCI for system reset at runtime

Since the default EfiResetSystemLib for VExpress cannot be used at
runtime (due to the fact that its MMIO registers need to be owned
by the OS and so cannot be runtime remapped), instead use PSCI calls
into EL3 at runtime.

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@17380 6f19259b-4bc3-4df7-8a09-765794883524