Add and use rtems_blkdev_request_done(). Block device transfer requests
must signal the completion status now with rtems_blkdev_request_done().
The return value of the block device IO control will be ignored for
transfer requests.
The first parameter of rtems_blkdev_request_cb is now the transfer
request structure.
Renamed rtems_blkdev_request::req_done to rtems_blkdev_request::done to
break third party drivers at compile time, otherwise this API change
would result in runtime errors.
