ARM: OMAP3: mmc-twl4030 add cover switch

Allow a cover switch to be used to cause a rescan of the
MMC slot.

Signed-off-by: Adrian Hunter <adrian.hunter@nokia.com>
Acked-by: David Brownell <dbrownell@users.sourceforge.net>
Signed-off-by: Tony Lindgren <tony@atomide.com>