Add parameters to the OMAP MMC initialization function so the board can
mask host capabilities and set the maximum clock frequency.  While the
OMAP supports a certain set of MMC host capabilities, individual boards
may be more restricted and the OMAP may need to be configured to match
the board.  The PRG_SDMMC1_SPEEDCTRL bit in the OMAP3 is an example.

Signed-off-by: Jonathan Solnit <jsolnit@gmail.com>