arm/dt: msm8974: Add regulator support for SDC controllers

SDC controllers need two types of power supply:
- vdd (SD/eMMC flash core power supply)
- vdd_io (SD/eMMC I/O pad power supply)

Add support for enable, disable, low power mode setting
for these regulators.

Change-Id: Ifd0ef0d4dd9732893f49700fe86b1dad24497f71
Signed-off-by: Sujit Reddy Thumma <sthumma@codeaurora.org>