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.
The set block size must synchronize and purge the disk to avoid an
inconsistent cache state and data corruption. The synchronization is
optional depending on the new sync parameter. In some contexts a
synchronization must not be performed, e.g. during disk creation.
