better handle "phy-mode" properties, in particular around clk delays.

better handle "phy-mode" properties, in particular around clk delays.

the phy mode can encode whether rk3568 mac should be doing the
delays when talking to the phy, or whether it should ignore them
and let the phy handle them. turns out this will probably be needed
by kettenis to get working ethernet on another rk3568 based system.

tweaks and ok kettenis@