s390/vfio-ap: Driver feature advertisement

Advertise features of the driver for the benefit of automated tooling
like Libvirt and mdevctl.

Signed-off-by: Jason J. Herne <jjherne@linux.ibm.com>
Reviewed-by: Anthony Krowiak <akrowiak@linux.ibm.com>
Reviewed-by: Boris Fiuczynski <fiuczy@linux.ibm.com>
Link: https://lore.kernel.org/r/20240916120123.11484-1-jjherne@linux.ibm.com


Signed-off-by: Heiko Carstens <hca@linux.ibm.com>
Signed-off-by: Vasily Gorbik <gor@linux.ibm.com>