OMAP3: RX51: Updated rx51_defconfig

Added REGULATOR, MMC and updated default CMDLINE so RX51 now boots.

Note that the regulator code should be moved from mmc-twl4030.c
to omap_hsmmc.c so it can be a module.

Signed-off-by: Roger Quadros <ext-roger.quadros@nokia.com>
Signed-off-by: Tony Lindgren <tony@atomide.com>