Implement software control for the internal delays of the RTL8211F PHY.

Implement software control for the internal delays of the RTL8211F PHY.
Since we need to retain the hardware/firmware configuration of the delays
in most existing hardware that uses rgephy(4) (such as PCIe NICs), add a
bew MIIF_SETDELAY flag that controls the software configuration of the
delays.

ok dlg@, jsg@