ramips: mt7621-dts: add pinctrl properties for ethernet

ramips: mt7621-dts: add pinctrl properties for ethernet

Add the missing pinctrl properties on the ethernet node.
GMAC1 will start working with this change.

Link: https://lore.kernel.org/netdev/[email protected]/
Overwrite pinctrl-0 property without rgmii2_pins on devicetrees which use
the rgmii2 pins as GPIO (22 - 33).

Give gpio function to rgmii2 pin group on mt7621_tplink_archer-x6-v3.dtsi
which uses GPIO 28.

Signed-off-by: Arınç ÜNAL <[email protected]>