Make the standard sdhci(4) driver work for the TI OMAP family SoCs.
The MMCHS hardware is pretty much a standard SDHCI v2.0 controller with a
couple quirks, which are now supported by sdhci(4) as of r254507.

This should work for all TI SoCs that use the MMCHS hardware, but it has
only been tested on AM335x right now, so this enables it on those platforms
but leaves the existing ti_mmchs driver in place for other OMAP variants
until they can be tested.

This initial incarnation lacks DMA support (coming soon).  Even without it
this improves performance pretty noticibly over the ti_mmchs driver,
primarily because it now does multiblock IO.