[SCSI] gdth: Move members from SCp to gdth_cmndinfo, stage 2

  - Cleanup the rest of the scsi_cmnd->SCp members and move them
    to gdth_cmndinfo:
    SCp.this_residual 	 => priority
    SCp.buffers_residual => timeout
    SCp.Status 		 => status and dma_dir
    SCp.Message 	 => info
    SCp.have_data_in 	 => volatile wait_for_completion
    SCp.sent_command 	 => OpCode
    SCp.phase 		 => phase

  - Two more members will be naturally removed in the !use_sg cleanup

  TODO: What is the meaning of gdth_cmndinfo.phase? (rhetorically)

Signed-off-by Boaz Harrosh <bharrosh@panasas.com>
Signed-off-by: James Bottomley <James.Bottomley@SteelEye.com>