feat(gicv5): add a barebones GICv5 driver

This is the absolute minimum that's needed to compile an NS-only build
end exit out of EL3. The GIC is not used and/or configured in any way
but all the necessary hooks are populated.

Notably, SCR_EL3.FIQ becomes RES1 as GICv5 behaves in a similar manner
to a GICv3 with FIQ set.

Change-Id: Idae52b9df97f4ca2996b2dcd1e5efc45478a43f2
Co-developed-by: Achin Gupta <achin.gupta@arm.com>
Signed-off-by: Boyan Karatotev <boyan.karatotev@arm.com>
7 files changed