KVM: arm64: Reenable pmu in Protected Mode

Now that the pmu code does not access hyp data, reenable it in
protected mode.

Once fully supported, protected VMs will not have pmu support,
since that could leak information. However, non-protected VMs in
protected mode should have pmu support if available.

Signed-off-by: Fuad Tabba <tabba@google.com>
Reviewed-by: Oliver Upton <oupton@google.com>
Signed-off-by: Marc Zyngier <maz@kernel.org>
Link: https://lore.kernel.org/r/20220510095710.148178-5-tabba@google.com