ArmPkg: cache detected revision in ArmGicArchLib

ArmPkg: cache detected revision in ArmGicArchLib

Instead of inferring the GIC revision from the CPU id registers
and the presence/availability of the system register interface
upon each invocation, move the logic to a constructor and cache
the result.

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@18100 6f19259b-4bc3-4df7-8a09-765794883524