msm: krypton: add gpio configuration for SD card regulator enable

The SD card slot is supplied by an external regulator controlled by MSM
GPIO 51. Add the gpiomux configuration in order to support this
function.

Change-Id: I945c064f990c4fe19325bcdafb542d732ba1b97c
Signed-off-by: Xiaozhe Shi <xiaozhes@codeaurora.org>