net: fec: register a fixed phy using fixed_phy_register_100fd if needed

net: fec: register a fixed phy using fixed_phy_register_100fd if needed

In case of coldfire/5272 a fixed phy is used, which so far is created
by platform code, using fixed_phy_add(). This function has a number of
problems, therefore create a potentially needed fixed phy here, using
fixed_phy_register_100fd.

Note 1: This includes a small functional change, as coldfire/5272
created a fixed phy in half-duplex mode. Likely this was by mistake,
because the fec MAC is 100FD-capable, and connection is to a switch.

Note 2: Usage of phy_find_next() makes use of the fact that dev_id can
only be 0 or 1.

Due to lack of hardware, this is compile-tested only.

Signed-off-by: Heiner Kallweit <hkallweit1@gmail.com>
Link: https://patch.msgid.link/adf4dc5c-5fa3-4ae6-a75c-a73954dede73@gmail.com
Signed-off-by: Jakub Kicinski <kuba@kernel.org>