mmc: tmio: split core functionality, DMA and MFD glue

TMIO MMC chips contain an SD / SDIO IP core from Panasonic, similar to
the one, used in MN5774 and other MN57xx controllers. These IP cores are
included in many multifunction devices, in sh-mobile chips from Renesas,
in the latter case they can also use DMA. Some sh-mobile implementations
also have some other specialities, that MFD-based solutions don't have.
This makes supporting all these features in a monolithic driver inconveniet
and error-prone. This patch splits the driver into 3 parts: the core,
the MFD glue and the DMA support. In case of a modular build, two modules
will be built: mmc_tmio_core and mmc_tmio.

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>