ARM: dts: msm: Add UFS vcc voltage level entry for sdm670

Allow selecting the UFS's vcc voltage level via device tree setting.
If the device tree does not specify the UFS vcc-voltage-level, the
default values specified in the driver code will be used.

Change-Id: Ic0c8f1000e63339410102d127bc32e039371d7fc
Signed-off-by: Sayali Lokhande <sayalil@codeaurora.org>