rpm: use PMDK system libraries on SUSE

rpm: use PMDK system libraries on SUSE

As of a49d1dbb32e2436ff2836a85b2fa84418f0a5fff, when the rbd_rwl_cache and
rbd_ssd_cache bconds are enabled and WITH_SYSTEM_PMDK is disabled (as it is by
default), the RPM build attempts to

    git clone https://github.com/ceph/pmdk.git

but of course that won't work in the OBS, where the build workers have no
Internet connectivity.

Fortunately, the openSUSE/SLE versions targeted by Ceph master and pacific ship
the necessary PMDK libraries as RPM packages.

Fixes: a49d1dbb32e2436ff2836a85b2fa84418f0a5fff
Fixes: https://tracker.ceph.com/issues/49550
Signed-off-by: Nathan Cutler <ncutler@suse.com>