KVM: arm64: Wrapper for getting pmu_events

Eases migrating away from using hyp data and simplifies the code.

No functional change intended.

Reviewed-by: Oliver Upton <oupton@google.com>
Signed-off-by: Fuad Tabba <tabba@google.com>
Signed-off-by: Marc Zyngier <maz@kernel.org>
Link: https://lore.kernel.org/r/20220510095710.148178-2-tabba@google.com