staging: mt7621-dts: use trgmii on gmac0 and enable flow control on port@6

Change phy-mode of gmac0 to trgmii to match the other side, port@6.

Flow control needs to be enabled on both sides to work.
It is already enabled on gmac0, enable it on port@6 too.

Reviewed-by: Sergio Paracuellos <sergio.paracuellos@gmail.com>
Signed-off-by: Arınç ÜNAL <arinc.unal@arinc9.com>
Link: https://lore.kernel.org/r/20220125153903.1469-4-arinc.unal@arinc9.com


Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>