staging: mt7621-dts: fix GB-PC2 devicetree

staging: mt7621-dts: fix GB-PC2 devicetree

Fix the GB-PC2 devicetree. Refer to the schematics of the device for more
information.

GB-PC2 devicetree fixes:
- Include mt7621.dtsi instead of gbpc1.dts. Add the missing definitions.
- Remove gpio-leds node as the system LED is not wired to anywhere on
the board and the power LED is directly wired to GND.
- Remove uart3 pin group from gpio-pinmux node as it's not used as GPIO.
- Use reg 7 for the external phy to be on par with
Documentation/devicetree/bindings/net/dsa/mt7530.txt.
- Use the status value "okay".

Link: https://github.com/ngiger/GnuBee_Docs/blob/master/GB-PCx/Documents/GB-PC2_V1.1_schematic.pdf
Reviewed-by: Sergio Paracuellos <sergio.paracuellos@gmail.com>
Signed-off-by: Arınç ÜNAL <arinc.unal@arinc9.com>
Link: https://lore.kernel.org/r/20220311090320.3068-2-arinc.unal@arinc9.com
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>