vfio/pds: Move and rename region specific info

An upcoming change in this series will add support
for multiple regions. To prepare for that, move
region specific information into struct pds_vfio_region
and rename the members for readability. This will
reduce the size of the patch that actually implements
multiple region support.

Signed-off-by: Brett Creeley <brett.creeley@amd.com>
Signed-off-by: Shannon Nelson <shannon.nelson@amd.com>
Link: https://lore.kernel.org/r/20231117001207.2793-4-brett.creeley@amd.com


Signed-off-by: Alex Williamson <alex.williamson@redhat.com>