board: lg-x3: convert LG Optimus 4X and Vu to use DM PMIC

Since required drivers were merged, we can safely clean up the
board and switch to DM based driver with device tree support.

Signed-off-by: Svyatoslav Ryhel <clamor95@gmail.com>
diff --git a/arch/arm/dts/tegra30-lg-x3.dtsi b/arch/arm/dts/tegra30-lg-x3.dtsi
index 6e52fc5..aa207a7 100644
--- a/arch/arm/dts/tegra30-lg-x3.dtsi
+++ b/arch/arm/dts/tegra30-lg-x3.dtsi
@@ -110,6 +110,7 @@
 					regulator-name = "vdd_ddr_rx";
 					regulator-min-microvolt = <2850000>;
 					regulator-max-microvolt = <2850000>;
+					regulator-boot-on;
 				};
 			};
 		};