KVM: selftests: arm64: Test writes to CTR_EL0

Test that CTR_EL0 is modifiable from userspace, that changes are
visible to guests, and that they are preserved across a vCPU reset.

Signed-off-by: Sebastian Ott <sebott@redhat.com>
Reviewed-by: Eric Auger <eric.auger@redhat.com>
Link: https://lore.kernel.org/r/20240619174036.483943-11-oliver.upton@linux.dev
Signed-off-by: Oliver Upton <oliver.upton@linux.dev>