sh: ecovec: switch MMC power control to regulators

Power on the CN11 and CN12 SD/MMC slots on ecovec is controlled by GPIOs,
which makes it possible to use the fixed voltage regulator driver to switch
card power on and off.

Signed-off-by: Guennadi Liakhovetski <g.liakhovetski@gmx.de>
Signed-off-by: Paul Mundt <lethal@linux-sh.org>