refactor(stm32mp1-fdts): update regulator description

Update regulator description to match with pmic driver updates.
vref_ddr does not support over-current protection.
vtt_ddr is set to sink source mode.

Change-Id: I725f35b091ca8c230994c2b5f81693ebc97bf4aa
Signed-off-by: Pascal Paillet <p.paillet@st.com>
Signed-off-by: Yann Gautier <yann.gautier@foss.st.com>

fdts/stm32mp157c-ed1.dts

@@ -135,14 +135,15 @@
 
 			vtt_ddr: ldo3 {
 				regulator-name = "vtt_ddr";
-				regulator-min-microvolt = <500000>;
-				regulator-max-microvolt = <750000>;
 				regulator-always-on;
 				regulator-over-current-protection;
+				st,regulator-sink-source;
 			};
 
 			vdd_usb: ldo4 {
 				regulator-name = "vdd_usb";
+				regulator-min-microvolt = <3300000>;
+				regulator-max-microvolt = <3300000>;
 			};
 
 			vdd_sd: ldo5 {

fdts/stm32mp15xx-dkx.dtsi

@@ -131,10 +131,9 @@
 
 			vtt_ddr: ldo3 {
 				regulator-name = "vtt_ddr";
-				regulator-min-microvolt = <500000>;
-				regulator-max-microvolt = <750000>;
 				regulator-always-on;
 				regulator-over-current-protection;
+				st,regulator-sink-source;
 			};
 
 			vdd_usb: ldo4 {
@@ -160,7 +159,6 @@
 			vref_ddr: vref_ddr {
 				regulator-name = "vref_ddr";
 				regulator-always-on;
-				regulator-over-current-protection;
 			};
 
 			bst_out: boost {