ARM: dts: at91: sama7g5ek: use proper slew-rate settings for GMACs

Datasheet chapter "EMAC Timings" specifies that while in 3.3V domain
GMAC's MDIO pins should be configured with slew-rate enabled, while the
data + signaling pins should be configured with slew-rate disabled when
GMAC works in RGMII or RMII modes. The pin controller for SAMA7G5 sets
the slew-rate as enabled for all pins. Adapt the device tree to comply
with these.

Fixes: 7540629e ("ARM: dts: at91: add sama7g5 SoC DT and sama7g5-ek")
Signed-off-by: Claudiu Beznea <claudiu.beznea@microchip.com>
Signed-off-by: Nicolas Ferre <nicolas.ferre@microchip.com>
Link: https://lore.kernel.org/r/20210915074836.6574-2-claudiu.beznea@microchip.com

arch/arm/boot/dts/at91-sama7g5ek.dts

@@ -355,7 +355,10 @@ &gmac0 {
 	#address-cells = <1>;
 	#size-cells = <0>;
 	pinctrl-names = "default";
-	pinctrl-0 = <&pinctrl_gmac0_default &pinctrl_gmac0_txck_default &pinctrl_gmac0_phy_irq>;
+	pinctrl-0 = <&pinctrl_gmac0_default
+		     &pinctrl_gmac0_mdio_default
+		     &pinctrl_gmac0_txck_default
+		     &pinctrl_gmac0_phy_irq>;
 	phy-mode = "rgmii-id";
 	status = "okay";
 
@@ -370,7 +373,9 @@ &gmac1 {
 	#address-cells = <1>;
 	#size-cells = <0>;
 	pinctrl-names = "default";
-	pinctrl-0 = <&pinctrl_gmac1_default &pinctrl_gmac1_phy_irq>;
+	pinctrl-0 = <&pinctrl_gmac1_default
+		     &pinctrl_gmac1_mdio_default
+		     &pinctrl_gmac1_phy_irq>;
 	phy-mode = "rmii";
 	status = "okay";
 
@@ -425,14 +430,20 @@ pinctrl_gmac0_default: gmac0_default {
 			 <PIN_PA15__G0_TXEN>,
 			 <PIN_PA30__G0_RXCK>,
 			 <PIN_PA18__G0_RXDV>,
-			 <PIN_PA22__G0_MDC>,
-			 <PIN_PA23__G0_MDIO>,
 			 <PIN_PA25__G0_125CK>;
+		slew-rate = <0>;
+		bias-disable;
+	};
+
+	pinctrl_gmac0_mdio_default: gmac0_mdio_default {
+		pinmux = <PIN_PA22__G0_MDC>,
+			 <PIN_PA23__G0_MDIO>;
 		bias-disable;
 	};
 
 	pinctrl_gmac0_txck_default: gmac0_txck_default {
 		pinmux = <PIN_PA24__G0_TXCK>;
+		slew-rate = <0>;
 		bias-pull-up;
 	};
 
@@ -449,8 +460,13 @@ pinctrl_gmac1_default: gmac1_default {
 			 <PIN_PD25__G1_RX0>,
 			 <PIN_PD26__G1_RX1>,
 			 <PIN_PD27__G1_RXER>,
-			 <PIN_PD24__G1_RXDV>,
-			 <PIN_PD28__G1_MDC>,
+			 <PIN_PD24__G1_RXDV>;
+		slew-rate = <0>;
+		bias-disable;
+	};
+
+	pinctrl_gmac1_mdio_default: gmac1_mdio_default {
+		pinmux = <PIN_PD28__G1_MDC>,
 			 <PIN_PD29__G1_MDIO>;
 		bias-disable;
 	};