ramips: enable external amplifier for D-Link DIR-810L

The 2.4 GHz radio had very poor signal reception (-89 dBm for an AP
sitting 5 m away). By enabling the external amplifier, received signal
has improved to -50 dBm for the same AP.

Signed-off-by: Roger Pueyo Centelles <roger.pueyo@guifi.net>
(cherry picked from commit e667d6f46b)

target/linux/ramips/dts/DIR-810L.dts

@@ -143,6 +143,8 @@
 
 &wmac {
 	ralink,mtd-eeprom = <&factory 0x0>;
+	pinctrl-names = "default";
+	pinctrl-0 = <&pa_pins>;
 	mtd-mac-address = <&factory 0x28>;
 };