smc911x_eeprom: fix building after smc911x overhaul

When the smc911x driver was converted to NET_MULTI, the smc911x eeprom was
missed.  The config option needed updating as well as overhauling of the
rergister read/write functions.

Signed-off-by: Mike Frysinger <vapier@gentoo.org>
Tested-by: Mike Rapoport <mike.rapoport@gmail.com>
Signed-off-by: Ben Warren <biggerbadderben@gmail.com>