mmc: tmio: convert the SDHI MMC driver from MFD to a platform driver

On sh-mobile platforms the SDHI driver was using the tmio_mmc SD/SDIO
MFD cell driver. Now that the tmio_mmc driver has been split into a
core and a separate MFD glue, we can support SDHI natively without the
need to emulate an MFD controller. This also allows to support systems
with an on-SoC SDHI controller and a separate MFD with a TMIO core.

Signed-off-by: Guennadi Liakhovetski <g.liakhovetski@gmx.de>
Acked-by: Paul Mundt <lethal@linux-sh.org>
Signed-off-by: Chris Ball <cjb@laptop.org>