[NET] Eliminate user-selectable CONFIG_MV643XX_ETH_[012]

Remove the use of CONFIG_MV643XX_ETH_[012] variables on most platforms.
Instead, platform-specific code enables the ports supported by the
hardware.  After this patch, these config variables are only used in
arch/ppc, so also move them from drivers/net/Kconfig to arch/ppc/Kconfig.

Signed-off-by: Dale Farnsworth <dale@farnsworth.org>
Signed-off-by: Ralf Baechle <ralf@linux-mips.org>
Acked-by: Jeff Garzik <jeff@garzik.org>
Cc: Paul Mackerras <paulus@samba.org>