Add MMC for 2420 so we can pass the DMA request lines the same
way as we already do on omap2430 and later.

Cc: Benoit Cousson <b-cousson@ti.com>
Cc: Paul Walmsley <paul@pwsan.com>
Signed-off-by: Tony Lindgren <tony@atomide.com>
[paul@pwsan.com: updated to apply on top of the 3.5 hwmod cleanup;
 changed mmc hwmod name/class to "msdi" as documented in the 2420 TRM Rev X;
 added sysconfig register information; added 16 bit register width flag;
 added MSDI custom reset code]
Signed-off-by: Paul Walmsley <paul@pwsan.com>