twl4030 MMC card detction

Replace stubbed-out card-detect support for twl4030 GPIOs with
a simpler platform_data mechanism.  As before, no current users.
Sanity tested by enabling this on Beagle; it booted OK with
root on MMC.

Signed-off-by: David Brownell <dbrownell@users.sourceforge.net>
Signed-off-by: Tony Lindgren <tony@atomide.com>