mmc: omap_hsmmc: Convert hsmmc driver to use device tree

Define dt bindings for the ti-omap-hsmmc, and adapt the driver to extract
data (which was earlier passed as platform_data) from device tree.

Signed-off-by: Rajendra Nayak <rnayak@ti.com>
Acked-by: Rob Herring <rob.herring@calxeda.com>
Signed-off-by: Chris Ball <cjb@laptop.org>