ArmVirtPkg: record GIC revision in dynamic PCD

ArmVirtPkg: record GIC revision in dynamic PCD

In order to allow a ArmGicArchLib to be implemented that returns
the supported GIC revision based on the device tree, add handling
to VirtFdtDxe to record the GIC revision at DT parsing time.

Contributed-under: TianoCore Contribution Agreement 1.0
Signed-off-by: Ard Biesheuvel <ard.biesheuvel@linaro.org>
Reviewed-by: Laszlo Ersek <lersek@redhat.com>
Reviewed-by: Leif Lindholm <leif.lindholm@linaro.org>
Tested-by: Leif Lindholm <leif.lindholm@linaro.org>
git-svn-id: https://svn.code.sf.net/p/edk2/code/trunk/edk2@18101 6f19259b-4bc3-4df7-8a09-765794883524