scsi: dt-bindings: ufs: Add VCC capability on MediaTek UFS driver

Add VCC supply for ufs-mediatek driver to provide power-saving operation
during low-power modes. For example VCC can be turned-off during system
suspend and turned-on after system is resumed.
Signed-off-by: Stanley Chu <stanley.chu@mediatek.com>
Signed-off-by: Martin K. Petersen <martin.petersen@oracle.com>

Documentation/devicetree/bindings/ufs/ufs-mediatek.txt

@@ -21,6 +21,7 @@ Required properties for UFS nodes:
                        defined or a value in the array is "0" then it is assumed
                        that the frequency is set by the parent clock or a
                        fixed rate clock source.
+- vcc-supply         : phandle to VCC supply regulator node.
 
 Example:
 
@@ -37,4 +38,6 @@ Example:
 		clocks = <&infracfg_ao INFRACFG_AO_UFS_CG>;
 		clock-names = "ufs";
 		freq-table-hz = <0 0>;
+
+		vcc-supply = <&mt_pmic_vemc_ldo_reg>;
 	};