Remove CONFIG_HAS_ETH0 et al symbols

This converts removes the following symbols:
   CONFIG_HAS_ETH0
   CONFIG_HAS_ETH1
   CONFIG_HAS_ETH2
   CONFIG_HAS_ETH3

This is because at this point, only the ids8313 platform was using the
code which was controlled by these symbols.  In turn, this code already
performs error checking on being able to perform the device tree fixup.
Rather than convert these to Kconfig for a single platform, update the
code to not need these checks and remove them from all the platforms
they were unused on.

Cc: Heiko Schocher <hs@denx.de>
Signed-off-by: Tom Rini <trini@konsulko.com>