ramips: mt7621-dts: do not claim rgmii2 group as gpio for certain devices

ramips: mt7621-dts: do not claim rgmii2 group as gpio for certain devices

These devices do not use rgmii2 as gpio, therefore remove rgmii2 pin group
from state-default. Remove overwriting the ethernet node for these devices.

Move claiming the rgmii2 group from mt7621_zyxel_nwa-ax.dtsi to
mt7621_zyxel_nwa50ax.dts as it's only the latter using rgmii2 pins as gpio.

Remove duplicate ethernet overwrite from mt7621_tplink_archer-x6-v3.dtsi.

Claim rgmii2 group as gpio on mt7621_bolt_arion.dts as it uses an rgmii2
pin, 26, as gpio.

Signed-off-by: Arınç ÜNAL <arinc.unal@arinc9.com>