selftests: ublk: add test case for UBLK_U_CMD_UPDATE_SIZE

Add test generic_10 for covering new control command of UBLK_U_CMD_UPDATE_SIZE.

Add 'update_size -s|--size size_in_bytes' sub-command on ublk utility for
supporting this feature, then verify the feature via generic_10.

Cc: Omri Mann <omri@nvidia.com>
Cc: Jared Holzman <jholzman@nvidia.com>
Signed-off-by: Ming Lei <ming.lei@redhat.com>
Link: https://lore.kernel.org/r/20250522163523.406289-2-ming.lei@redhat.com


Signed-off-by: Jens Axboe <axboe@kernel.dk>