FROMGIT: KVM: arm64: Fix AArch32 PMUv3 capping

We shouldn't expose *any* PMU capability when no PMU has been
configured for this VM.

Reviewed-by: Eric Auger <eric.auger@redhat.com>
Reviewed-by: Alexandru Elisei <alexandru.elisei@arm.com>
Signed-off-by: Marc Zyngier <maz@kernel.org>
(cherry picked from commit cb959146
 git://git.kernel.org/pub/scm/linux/kernel/git/kvmarm/kvmarm.git

 next)
Signed-off-by: Will Deacon <willdeacon@google.com>
Change-Id: I59a410fc2390f407ff8dd5ecf6883e0a4428cb9f
Bug: 178098380
Test: atest VirtualizationHostTestCases on an EL2-enabled device