ARM: dt: imx28-cfa10036: introduce a regulator for mmc0

The PWM3 pinmux configuration conflicts with gpio 3.28. Introduce a regulator
for mmc0 so that it conflicts with the pwm driver and fails gracefully. The
kernel will then able to access mmc0 normally.

Signed-off-by: Alexandre Belloni <alexandre.belloni@free-electrons.com>
Signed-off-by: Shawn Guo <shawn.guo@freescale.com>