arm64: compat: Add cp15_32 and cp15_64 handler arrays

We're now ready to start handling CP15 access. Let's add (empty)
arrays for both 32 and 64bit accessors, and the code that deals
with them.

Reviewed-by: Mark Rutland <mark.rutland@arm.com>
Signed-off-by: Marc Zyngier <marc.zyngier@arm.com>
Signed-off-by: Catalin Marinas <catalin.marinas@arm.com>