KVM: arm64: Use MDCR_EL2.HPME to evaluate overflow of hyp counters

The 'global enable control' (as it is termed in the architecture) for
counters reserved by EL2 is MDCR_EL2.HPME. Use that instead of
PMCR_EL0.E when evaluating the overflow state for hyp counters.

Change the return value to a bool while at it, which better reflects the
fact that the overflow state is a shared signal and not a per-counter
property.

Reviewed-by: Marc Zyngier <maz@kernel.org>
Link: https://lore.kernel.org/r/20241120005230.2335682-3-oliver.upton@linux.dev


Signed-off-by: Oliver Upton <oliver.upton@linux.dev>