ARM: dts: msm: add SD card regulator devices for sdxprairie

Add regulator devices for the external gpio-controlled regulators
which power the SD card slot on sdxprairie boards.

Change-Id: Ie8ef9bb9d6c59a90e8cdfe00409f36ca20c2609c
Signed-off-by: David Collins <collinsd@codeaurora.org>