dts: mtmips: add alternative pinmux node for uart2

This patch adds a new pinmux for UART2, which shares the pins with SPIS.

Reviewed-by: Stefan Roese <sr@denx.de>
diff --git a/arch/mips/dts/mt7628a.dtsi b/arch/mips/dts/mt7628a.dtsi
index 409695b..2200135 100644
--- a/arch/mips/dts/mt7628a.dtsi
+++ b/arch/mips/dts/mt7628a.dtsi
@@ -110,6 +110,11 @@
 				function = "uart2";
 			};
 
+			uart2_pwm_pins: uart2_pwm_pins {
+				groups = "spis";
+				function = "pwm_uart2";
+			};
+
 			i2c_pins: i2c_pins {
 				groups = "i2c";
 				function = "i2c";