arm: add support for supplying GICv3 redistributor addresses

Instead of the GIC virtual CPU interface an emulated GICv3 needs to
have accesses to its emulated redistributors trapped in the guest.
Add code to tell the kernel about the mapping if a GICv3 emulation was
requested by the user.

This contains some defines which are not (yet) in the (32 bit) header
files to allow compilation for ARM.

Signed-off-by: Andre Przywara <andre.przywara@arm.com>
Reviewed-by: Marc Zyngier <marc.zyngier@arm.com>
Signed-off-by: Will Deacon <will.deacon@arm.com>