configs: net: dm9000: Move new Kconfig option to board configs

Drop legacy #define CONFIG_DRIVER_DM9000 from board include/configs/
and enable the same in Kconfig configs/ .

Signed-off-by: Marek Vasut <marex@denx.de>
Cc: Joe Hershberger <joe.hershberger@ni.com>
Cc: Ramon Fried <rfried.dev@gmail.com>
Reviewed-by: Ramon Fried <rfried.dev@gmail.com>