ARM: OMAP: hsmmc: Add support for non-OMAP pins

The Devkit8000 uses a TWL4030 pin for card detection.
Thats why the error:
_omap_mux_init_gpio: Could not set gpio192
occurs.

This patch checks that the pin is on OMAP before
calling omap_mux_init_gpio.

Signed-off-by: Thomas Weber <weber@corscience.de>
[tony@atomide.com: updated comments]
Signed-off-by: Tony Lindgren <tony@atomide.com>