omap: mmc: extended to pass host capabilities from board file

wires variable is renamed, extended and this single variable to be used to
pass the platform capabilities, e.g DDR mode. Also removed the hardcoded
value was using as bus-width.

Signed-off-by: Sukumar Ghorai <s-ghorai@ti.com>
Signed-off-by: Tony Lindgren <tony@atomide.com>