ARM: dts: msm: add SD card regulator for msmzirc

The SD card regulator is an external LDO controlled by MSM GPIO 50.
This regulator is always on when eMMC is enabled on the CDP but can
be controlled by the GPIO when nand is enabled on the CDP.

Change-Id: I210b8d1d59cd9512ae0c3f4a592bfe307c864157
Signed-off-by: Krishna Konda <kkonda@codeaurora.org>