ARM: dts: imx6sll-evk: make pfuze100 sw4 always on

On i.MX6SLL EVK board, pfuze100 sw4 supplies
LPDDR3 which is critical for system, must be
always on.
Signed-off-by: Anson Huang <Anson.Huang@nxp.com>
Signed-off-by: Shawn Guo <shawnguo@kernel.org>

arch/arm/boot/dts/imx6sll-evk.dts

@@ -177,6 +177,7 @@ sw3b_reg: sw3b {
 			sw4_reg: sw4 {
 				regulator-min-microvolt = <800000>;
 				regulator-max-microvolt = <3300000>;
+				regulator-always-on;
 			};
 
 			swbst_reg: swbst {