This patch does a few simple compatibility-related changes:
- change the system register access prototypes to their actual size,
- homogenise mpidr accesses with unsigned long,
- force the 64bit register values to unsigned long long.

Note: the list registers are 64bit on GICv3, but the AArch32 vGIC driver
will need to split their values into two 32bit registers: LRn and LRCn.
Reviewed-by: NMarc Zyngier <marc.zyngier@arm.com>
Signed-off-by: NJean-Philippe Brucker <jean-philippe.brucker@arm.com>
Signed-off-by: NMarc Zyngier <marc.zyngier@arm.com>