hw/intc/arm_gicv3: report correct PRIbits field in ICV_CTLR_EL1

hw/intc/arm_gicv3: report correct PRIbits field in ICV_CTLR_EL1

As noted in the comment, the PRIbits field in ICV_CTLR_EL1 is
supposed to match the ICH_VTR_EL2 PRIbits setting; that is, it is the
virtual priority bit setting, not the physical priority bit setting.
(For QEMU currently we always implement 8 bits of physical priority,
so the PRIbits field was previously 7, since it is defined to be
"priority bits - 1".)

Signed-off-by: Peter Maydell <[email protected]>
Reviewed-by: Richard Henderson <[email protected]>
Message-id: 20220512151457.3899052[email protected]
Message-id: 20220506162129.2896966[email protected]