ARM: dts: sun6i: Add pin muxing options for GMAC

The A31 SoC has a GMAC gigabit ethernet controller supporting
MII, GMII, RGMII modes. Add pin muxing options for these modes.
Signed-off-by: Chen-Yu Tsai <wens@csie.org>
Signed-off-by: Maxime Ripard <maxime.ripard@free-electrons.com>

arch/arm/boot/dts/sun6i-a31.dtsi

@@ -467,6 +467,48 @@ mmc0_pins_a: mmc0@0 {
 				allwinner,drive = <2>;
 				allwinner,pull = <0>;
 			};
+
+			gmac_pins_mii_a: gmac_mii@0 {
+				allwinner,pins = "PA0", "PA1", "PA2", "PA3",
+						"PA8", "PA9", "PA11",
+						"PA12", "PA13", "PA14", "PA19",
+						"PA20", "PA21", "PA22", "PA23",
+						"PA24", "PA26", "PA27";
+				allwinner,function = "gmac";
+				allwinner,drive = <0>;
+				allwinner,pull = <0>;
+			};
+
+			gmac_pins_gmii_a: gmac_gmii@0 {
+				allwinner,pins = "PA0", "PA1", "PA2", "PA3",
+						"PA4", "PA5", "PA6", "PA7",
+						"PA8", "PA9", "PA10", "PA11",
+						"PA12", "PA13", "PA14",	"PA15",
+						"PA16", "PA17", "PA18", "PA19",
+						"PA20", "PA21", "PA22", "PA23",
+						"PA24", "PA25", "PA26", "PA27";
+				allwinner,function = "gmac";
+				/*
+				 * data lines in GMII mode run at 125MHz and
+				 * might need a higher signal drive strength
+				 */
+				allwinner,drive = <2>;
+				allwinner,pull = <0>;
+			};
+
+			gmac_pins_rgmii_a: gmac_rgmii@0 {
+				allwinner,pins = "PA0", "PA1", "PA2", "PA3",
+						"PA9", "PA10", "PA11",
+						"PA12", "PA13", "PA14", "PA19",
+						"PA20", "PA25", "PA26", "PA27";
+				allwinner,function = "gmac";
+				/*
+				 * data lines in RGMII mode use DDR mode
+				 * and need a higher signal drive strength
+				 */
+				allwinner,drive = <3>;
+				allwinner,pull = <0>;
+			};
 		};
 
 		ahb1_rst: reset@01c202c0 {