ipq806x: update Netgear R7800 device tree

-add spi pins
-move mdio and rgmii pinctrl from gmac and mdio into pinmux node
-add i2c4 pinctrl into rpm node
-add pin details into several nodes
-update gmac1 and gmac2 parameters
-update mdio phy0 and phy4 registers by ddwrt devs findings
-fix i2c4 pin drive-strengh
-remove pcie pins as it's already present in ipq8065 DT

Signed-off-by: Pavel Kubelun <be.dissent@gmail.com>