arm64: sysreg: subsume GICv3 sysreg definitions

Unlike most sysreg defintiions, the GICv3 definitions don't have a SYS_
prefix, and they don't live in <asm/sysreg.h>. Additionally, some
definitions are duplicated elsewhere (e.g. in the KVM save/restore
code).

For consistency, and to make it possible to share a common definition
for these sysregs, this patch moves the definitions to <asm/sysreg.h>,
adding a SYS_ prefix, and sorting the registers per their encoding.
Existing users of the definitions are fixed up so that this change is
not problematic.

Signed-off-by: Mark Rutland <mark.rutland@arm.com>
Cc: Catalin Marinas <catalin.marinas@arm.com>
Cc: Marc Zyngier <marc.zyngier@arm.com>
Cc: Suzuki K Poulose <suzuki.poulose@arm.com>
Cc: Will Deacon <will.deacon@arm.com>