netdev: bfin_mac: push settings to platform resources

Move all the pin settings out of the Kconfig and into the platform
resources (MII vs RMII).  This clean up also lets us push out the
phy settings so that board porters may control the layout.

Signed-off-by: Sonic Zhang <sonic.zhang@analog.com>
Acked-by: David S. Miller <davem@davemloft.net>
Signed-off-by: Mike Frysinger <vapier@gentoo.org>