hw/arm/virt: fix PMU IRQ registration

Since commit 9036e917 ("{include/}hw/arm: refactor virt PPI logic")
PMU IRQ registration fails for arm64 guests:

[    0.563689] hw perfevents: unable to request IRQ14 for ARM PMU counters
[    0.565160] armv8-pmu: probe of pmu failed with error -22

That commit re-defined VIRTUAL_PMU_IRQ to be a INTID but missed a case
where the PMU IRQ is actually referred by its PPI index. Fix that by using
INTID_TO_PPI() in that case.

Fixes: 9036e917 ("{include/}hw/arm: refactor virt PPI logic")
Resolves: https://gitlab.com/qemu-project/qemu/-/issues/1960


Signed-off-by: Sebastian Ott <sebott@redhat.com>
Reviewed-by: Peter Maydell <peter.maydell@linaro.org>
Message-id: 475d918d-ab0e-f717-7206-57a5beb28c7b@redhat.com
Signed-off-by: Peter Maydell <peter.maydell@linaro.org>