hw/intc/arm_gicv3_redist: Recalculate hppvlpi on VPENDBASER writes

hw/intc/arm_gicv3_redist: Recalculate hppvlpi on VPENDBASER writes

The guest uses GICR_VPENDBASER to tell the redistributor when it is
scheduling or descheduling a vCPU.  When it writes and changes the
VALID bit from 0 to 1, it is scheduling a vCPU, and we must update
our view of the current highest priority pending vLPI from the new
Pending and Configuration tables.  When it writes and changes the
VALID bit from 1 to 0, it is descheduling, which means that there is
no longer a highest priority pending vLPI.

The specification allows the implementation to use part of the vLPI
Pending table as an IMPDEF area where it can cache information when a
vCPU is descheduled, so that it can avoid having to do a full rescan
of the tables when the vCPU is scheduled again.  For now, we don't
take advantage of this, and simply do a complete rescan.

Signed-off-by: Peter Maydell <peter.maydell@linaro.org>
Reviewed-by: Richard Henderson <richard.henderson@linaro.org>
Message-id: 20220408141550.1271295-30-peter.maydell@linaro.org