Handle fixed-link configuration in the device tree.

Handle fixed-link configuration in the device tree.

If fixed-link is present, populate the interface baudrate, link status
(full duplex or half duplex) and media type, and then call the statch
handler to apply that config to the MAC.  If fixed-link is specified
then do not attach a phy.

Note that phy lookup and reset still occurs in case the device tree
still uses the deprecated snps,reset-gpio properties.

Based on if_dwqe_fdt.c v1.11 and dwqe.c v1.8.
Tested on a Banana Pi R1 (aka Lamobo R1), which has its dwge interface
connected directly to an ethernet switch.

ok kettenis@