ARMV8_PMU_PMCR_N_MASK is an unshifted value which results in the wrong
reset value for PMCR_EL0, so shift it to fix it.

This fixes the following error when running qemu:

  $ qemu-system-aarch64 -cpu host -machine type=virt,accel=kvm -kernel ...

  target/arm/helper.c:1813: pmevcntr_rawwrite: Assertion `counter < pmu_num_counters(env)' failed.

Fixes: 292e8f14 ("KVM: arm64: PMU: Simplify PMCR_EL0 reset handling")
Signed-off-by: James Clark <james.clark@arm.com>
Reviewed-by: Oliver Upton <oliver.upton@linux.dev>
Signed-off-by: Marc Zyngier <maz@kernel.org>
Link: https://lore.kernel.org/r/20221209164446.1972014-2-james.clark@arm.com