ide_raw_taskfile() directly uses rq->buffer to carry pointer to the
data buffer. This complicates both block interface and ide backend
request handling. Use blk_rq_map_kern() instead and drop special
handling for REQ_TYPE_ATA_TASKFILE from ide_map_sg().
Note that REQ_RW setting is moved upwards as blk_rq_map_kern() uses it
to initialize bio rw flag.