s390/vfio-ap: Add sysfs attr, ap_config, to export mdev state

s390/vfio-ap: Add sysfs attr, ap_config, to export mdev state

Add ap_config sysfs attribute. This will provide the means for
setting or displaying the adapters, domains and control domains assigned
to the vfio-ap mediated device in a single operation. This sysfs
attribute is comprised of three masks: One for adapters, one for domains,
and one for control domains.

This attribute is intended to be used by mdevctl to query a vfio-ap
mediated device's state.

Signed-off-by: "Jason J. Herne" <jjherne@linux.ibm.com>
Reviewed-by: Tony Krowiak <akrowiak@linux.ibm.com>
Tested-by: Matthew Rosato <mjrosato@linux.ibm.com>
Link: https://lore.kernel.org/r/20240415152555.13152-3-jjherne@linux.ibm.com
Signed-off-by: Alexander Gordeev <agordeev@linux.ibm.com>