Support these transfer modes from the SPI layer by setting
the appropriate register bits before doing the transfer.

This was tested on the Marvell kirkwood SOC that uses this driver.
Reviewed-by: Jason Gunthorpe <jgunthorpe@obsidianresearch.com>
Signed-off-by: Rolf Manderscheid <rvm@obsidianresearch.com>
Signed-off-by: Grant Likely <grant.likely@secretlab.ca>