ArmPkg/ArmGicLib: manage GICv3 SPI state at the distributor

ArmPkg/ArmGicLib: manage GICv3 SPI state at the distributor

Unlike SGIs and PPIs, which are private to the CPU and are managed at
the redistributor level (which is also a per-CPU construct), shared
interrupts (SPIs) are shared between all CPUs, and therefore managed at
the distributor level (just as on GICv2).

Reported-by: Narinder Dhillon <ndhillonv2@gmail.com>
Contributed-under: TianoCore Contribution Agreement 1.0
Signed-off-by: Ard Biesheuvel <ard.biesheuvel@linaro.org>
Reviewed-by: Leif Lindholm <leif.lindholm@linaro.org>