mxs: spi: Fix the MXS SPI for mx23

The MX23 has slightly different register layout. Adjust the SPI
driver to match the layout, both the PIO and DMA part.

Signed-off-by: Marek Vasut <marex@denx.de>
Cc: Fabio Estevam <fabio.estevam@freescale.com>
Cc: Otavio Salvador <otavio@ossystems.com.br>
Cc: Stefano Babic <sbabic@denx.de>