net: phy: fixed_phy: remove fixed_phy_add

net: phy: fixed_phy: remove fixed_phy_add

fixed_phy_add() has a number of problems/disadvantages:
- It uses phy address 0 w/o checking whether a fixed phy with this
  address exists already.
- A subsequent call to fixed_phy_register() would also use phy address 0,
  because fixed_phy_add() doesn't mark it as used.
- fixed_phy_add() is used from platform code, therefore requires that
  fixed_phy code is built-in.

Now that for the only two users (coldfire/5272 and bcm47xx) fixed_phy
creation has been moved to the respective ethernet driver (fec, b44),
we can remove fixed_phy_add().

Signed-off-by: Heiner Kallweit <hkallweit1@gmail.com>
Link: https://patch.msgid.link/bee046a1-1e77-4057-8b04-fdb2a1bbbd08@gmail.com
Signed-off-by: Jakub Kicinski <kuba@kernel.org>