vfio/xe: Add default handler for .get_region_info_caps

vfio/xe: Add default handler for .get_region_info_caps

New requirement for the vfio drivers was added by the commit
f97859503859 ("vfio: Require drivers to implement get_region_info")
followed by commit 1b0ecb5baf4a ("vfio/pci: Convert all PCI drivers
to get_region_info_caps") that was missed by the new vfio/xe driver.

Add handler for .get_region_info_caps to avoid -EINVAL errors.

Fixes: 2e38c50ae492 ("vfio/xe: Add device specific vfio_pci driver variant for Intel graphics")
Signed-off-by: Michal Wajdeczko <michal.wajdeczko@intel.com>
Reviewed-by: Marcin Bernatowicz <marcin.bernatowicz@linux.intel.com>
Tested-by: Marcin Bernatowicz <marcin.bernatowicz@linux.intel.com>
Link: https://lore.kernel.org/r/20251218205106.4578-1-michal.wajdeczko@intel.com
Signed-off-by: Alex Williamson <alex@shazbot.org>