DaVinci Ethernet cleanup

Chips without the EMAC controller won't need the utilities
it uses to read an Ethernet address from EEPROM; so don't
include them needlessly.

Use is_valid_ether() to validate the address from EEPROM.
All-zero addresses aren't the only invalid addresses.
A fully erased EEPROM returns all-ones, also invalid...

Switch those Ethernet utilities to use "%pM" for printing
MAC addresses; and not say ROM when they mean EEPROM.

Signed-off-by: David Brownell <dbrownell@users.sourceforge.net>
Acked-by: Ben Warren <biggerbadderben@gmail.com>