staging: mt7621-dts: do not use rgmii2_pins for ethernet on GB-PC1

staging: mt7621-dts: do not use rgmii2_pins for ethernet on GB-PC1

GB-PC1 uses some of the rgmii2 pins (22 - 33) as GPIO. Therefore, the
rgmii2 bus cannot be used on this device.
Overwrite pinctrl-0 property under the ethernet node without rgmii2_pins on
the GB-PC1 devicetree.

Tested-by: Sergio Paracuellos <sergio.paracuellos@gmail.com>
Signed-off-by: Arınç ÜNAL <arinc.unal@arinc9.com>
Link: https://lore.kernel.org/r/20220215081725.3463-2-arinc.unal@arinc9.com
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>