ArmPkg: allow dynamic GIC base addresses

ArmPkg: allow dynamic GIC base addresses

Allow the PCDs gArmTokenSpaceGuid.PcdGicDistributorBase and
gArmTokenSpaceGuid.PcdGicInterruptInterfaceBase to be redeclared
as PcdsDynamic by the platform, so virtual machines can set these
properties during boot. As the PcdGet32() calls now call into the
PCD database, cache the values that are required during the handling
of interrupts.

Contributed-under: TianoCore Contribution Agreement 1.0
Acked-by: Laszlo Ersek <lersek@redhat.com>
Signed-off-by: Ard Biesheuvel <ard.biesheuvel@linaro.org>
Signed-off-by: Olivier Martin <olivier.martin@arm.com>
git-svn-id: https://svn.code.sf.net/p/edk2/code/trunk/edk2@16072 6f19259b-4bc3-4df7-8a09-765794883524