All MXS users have been converted to device tree and the board files have
been removed.

No need to keep platform data in the driver.

Also move bus_width declaration in the beggining of mxs_mmc_probe() to
avoid: 'warning: ISO C90 forbids mixed declarations and code'.
Signed-off-by: NFabio Estevam <fabio.estevam@freescale.com>
Acked-by: NShawn Guo <shawn.guo@linaro.org>
Acked-by: NMarek Vasut <marex@denx.de>
Signed-off-by: NChris Ball <cjb@laptop.org>