dm vdo: add geometry block initialization to encodings.c

dm vdo: add geometry block initialization to encodings.c

Add vdo_initialize_volume_geometry() to populate the geometry block,
computing the space required for the two main regions on disk.

Add uds_compute_index_size() to calculate the space required for the
UDS indexer from the UDS configuration.

Signed-off-by: Bruce Johnston <bjohnsto@redhat.com>
Reviewed-by: Matthew Sakai <msakai@redhat.com>
Signed-off-by: Mikulas Patocka <mpatocka@redhat.com>