arm64: kvm: Adopt new alternative assembler macros

Convert the dynamic patching for ARM64_HAS_SYSREG_GIC_CPUIF over to
the newly added alternative assembler macros.

Acked-by: Marc Zyngier <marc.zyngier@arm.com>
Signed-off-by: Daniel Thompson <daniel.thompson@linaro.org>
Signed-off-by: Will Deacon <will.deacon@arm.com>