At this moment mt7620 ethernet driver doesn't support rgmii delays
configuration. SoC MT7620 have bits 2 and 3 in GPC1 an GPC2 to configure
delays for rx and tx rgmii interface.
This patch adds rx/tx rgmii delay configuration from dts.
Signed-off-by: Pawel Dembicki <paweldembicki@gmail.com>