KVM: arm64: Add helpers to determine if PMC counts at a given EL

Checking the exception level filters for a PMC is a minor annoyance to
open code. Add helpers to check if an event counts at EL0 and EL1, which
will prove useful in a subsequent change.

Reviewed-by: Marc Zyngier <maz@kernel.org>
Link: https://lore.kernel.org/r/20241025182354.3364124-15-oliver.upton@linux.dev


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