Document how to modify the Broadwell refcode to support
the Intel GbE device.
Change-Id: I4f4f1e1c4ec2d79b3eb9f9c35fdc0330208e8509
Signed-off-by: Iru Cai <mytbk920423@gmail.com>
Reviewed-on: https://review.coreboot.org/c/coreboot/+/75418
Reviewed-by: Felix Singer <service+coreboot-gerrit@felixsinger.de>
Tested-by: build bot (Jenkins) <no-reply@coreboot.org>