arm/arm64: KVM: wrap 64 bit MMIO accesses with two 32 bit ones

Some GICv3 registers can and will be accessed as 64 bit registers.
Currently the register handling code can only deal with 32 bit
accesses, so we do two consecutive calls to cover this.

Signed-off-by: Andre Przywara <andre.przywara@arm.com>
Reviewed-by: Christoffer Dall <christoffer.dall@linaro.org>
Acked-by: Marc Zyngier <marc.zyngier@arm.com>
Signed-off-by: Christoffer Dall <christoffer.dall@linaro.org>