ARM: dts: am3517-evm-uboot: Add reg-shift for UART

With the resync of the omap3.dtsi file, the reg-shift was removed
so it breaks the UART.  Adding the reg-shift into the
am3517-evm-u-boot.dtsi keeps the reg-shift for U-Boot, but keeps
the dts/dtsi files clean from Linux.
Signed-off-by: NAdam Ford <aford173@gmail.com>

arch/arm/dts/am3517-evm-u-boot.dtsi

@@ -9,3 +9,15 @@
 		stdout-path = &uart3;
 	};
 };
+
+&uart1 {
+	reg-shift = <2>;
+};
+
+&uart2 {
+	reg-shift = <2>;
+};
+
+&uart3 {
+	reg-shift = <2>;
+};