irqchip/gic-v3-its: Change unsigned types for AArch32 compatibility

Make sure that constants which are supposed to be applied on 64-bit
data is actually unsigned long long, so they won't be truncated when
used in 32-bit mode.

Signed-off-by: Vladimir Murzin <vladimir.murzin@arm.com>
Signed-off-by: Marc Zyngier <marc.zyngier@arm.com>