ARM: sun7i: a20-olinuxino: Enable UARTs muxing

Instead of relying on the bootloader to mux the UART pins properly, do
it on our own and register the rightful pins for the A20-olinuxino in
the DT using pinctrl.
Signed-off-by: NMaxime Ripard <maxime.ripard@free-electrons.com>

arch/arm/boot/dts/sun7i-a20-olinuxino-micro.dts

@@ -20,14 +20,20 @@
 
 	soc@01c00000 {
 		uart0: serial@01c28000 {
+			pinctrl-names = "default";
+			pinctrl-0 = <&uart0_pins_a>;
 			status = "okay";
 		};
 
 		uart6: serial@01c29800 {
+			pinctrl-names = "default";
+			pinctrl-0 = <&uart6_pins_a>;
 			status = "okay";
 		};
 
 		uart7: serial@01c29c00 {
+			pinctrl-names = "default";
+			pinctrl-0 = <&uart7_pins_a>;
 			status = "okay";
 		};
 	};