UPSTREAM: arm64: alternative: Introduce feature for GICv3 CPU interface

Add a new item to the feature set (ARM64_HAS_SYSREG_GIC_CPUIF)
to indicate that we have a system register GIC CPU interface

This will help KVM switching to alternative instruction patching.

Reviewed-by: Andre Przywara <andre.przywara@arm.com>
Reviewed-by: Christoffer Dall <christoffer.dall@linaro.org>
Acked-by: Will Deacon <will.deacon@arm.com>
Signed-off-by: Marc Zyngier <marc.zyngier@arm.com>
Signed-off-by: Catalin Marinas <catalin.marinas@arm.com>

Bug: 31432001
Change-Id: If63cd4c166c8ee1406330c617921c8b395e7d953
(cherry picked from commit 94a9e04aa16abd1194d9b4158c618ba87f5d01e6)
Signed-off-by: Sami Tolvanen <samitolvanen@google.com>