Convert SMC911X Ethernet driver to CONFIG_NET_MULTI API

All in-tree boards that use this controller have CONFIG_NET_MULTI added
Also:
 - changed CONFIG_DRIVER_SMC911X* to CONFIG_SMC911X*
 - cleaned up line lengths
 - modified all boards that override weak function in this driver
 - added

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