hw/mips_gic: Update pin state on mask changes

If the GIC interrupt mask is changed by a write to the smask (set mask)
or rmask (reset mask) registers, we need to re-evaluate the state of the
pins/IRQs fed to the CPU. Without doing so we risk leaving a pin high
despite the interrupt that led to that state being masked, or losing
interrupts if an already pending interrupt is unmasked.

Signed-off-by: Paul Burton <paul.burton@imgtec.com>
Reviewed-by: Leon Alrae <leon.alrae@imgtec.com>
Signed-off-by: Yongbok Kim <yongbok.kim@imgtec.com>