staging: mt7621-dts: fix pinctrl properties for ethernet

staging: mt7621-dts: fix pinctrl properties for ethernet

Add pinctrl properties with rgmii1 & mdio pins under ethernet node which
was wrongfully put under an external phy node.
GMAC1 will start working with this fix.

Link: https://lore.kernel.org/netdev/02ecce91-7aad-4392-c9d7-f45ca1b31e0b@arinc9.com/T/
Move GB-PC2 specific phy_external node to its own device tree.

Reviewed-by: Sergio Paracuellos <sergio.paracuellos@gmail.com>
Signed-off-by: Arınç ÜNAL <arinc.unal@arinc9.com>
Link: https://lore.kernel.org/r/20220125153903.1469-5-arinc.unal@arinc9.com
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>