hw/arm_gic_common: Correct GICC_PMR reset value for newer GICs

hw/arm_gic_common: Correct GICC_PMR reset value for newer GICs

The GIC architecture specification for v1 and v2 GICs (as found
on the Cortex-A9 and newer) states that the GICC_PMR reset value
is zero; this differs from the 0xf0 reset value used on 11MPCore.
The NVIC is different again in not having a CPU interface; since
we share the GIC code we must force the priority mask field to
allow through all interrupts.

Signed-off-by: Peter Maydell <peter.maydell@linaro.org>
Reviewed-by: Igor Mitsyanko <i.mitsyanko@samsung.com>