lan91c96/smc91111/smc911x: get mac address from environment

lan91c96/smc91111/smc911x: get mac address from environment

The environment is the canonical storage location of the mac address, so
we're killing off the global data location and moving everything to
querying the env directly.

Also, do not bother checking the EEPROM if the env is setup.  This
simplifies the code greatly.

Signed-off-by: Mike Frysinger <[email protected]>
Signed-off-by: Wolfgang Dnek <[email protected]>
CC: Ben Warren <[email protected]>
CC: Rolf Offermanns <[email protected]>
CC: Erik Stahlman <[email protected]>
CC: Daris A Nevil <[email protected]>
CC: Sascha Hauer <[email protected]>