vfio-ap: flag as compatible with balloon

vfio-ap: flag as compatible with balloon

vfio-ap devices do not pin any pages in the host. Therefore, they
are compatible with memory ballooning.

Flag them as compatible, so both vfio-ap and a balloon can be
used simultaneously.

Cc: qemu-stable@nongnu.org
Acked-by: Christian Borntraeger <borntraeger@de.ibm.com>
Tested-by: Tony Krowiak <akrowiak@linux.ibm.com>
Reviewed-by: Halil Pasic <pasic@linux.ibm.com>
Signed-off-by: Cornelia Huck <cohuck@redhat.com>
(cherry picked from commit 1883e8fc8005e9ef452890a075bae98e8c432968)
Signed-off-by: Michael Roth <mdroth@linux.vnet.ibm.com>