AMD Inagua: add GEC firmware, document Broadcom BCM57xx Selfboot Patch format

The Broadcom BCM5785 GbE MAC integrated in the AMD Hudson-E1 requires a
secret sauce firmware blob to work.  As Broadcom wasn't willing to send us
any documentation (or a firmware adapted to our Micrel PHY) I had to figure
out everything by myself in many weeks of hard detective work.

In the end we had to settle for a different solution, the modified firmware
I devised for the Micrel KSZ9021 PHY on our early FrontRunner-AF prototypes
is no longer needed for the production version.  However the information
contained here might be very useful for others who'd like to use a
competing PHY instead of Broadcom's 50610, so it should not get lost.

And of course the unmodified, but now in large parts documented Selfboot
Patch is needed to get Ethernet on AMD Inagua.  The code introduced here
should make the Hudson's internal MAC usable without having to add the
proprietary firmware blob. - At least in theory.

Unfortunately we've been unable to actually test this patch on Inagua,
therefore the broadcom_init() call in mainboard.c was left commented out.
If you have the hardware and can confirm it works please enable it.

The fun thing is: as Broadcom refused to do any business with us at all,
or send us any documentation, we never had to sign an NDA with them.  This
leaves me free to publish everything I have found out.  :-)

Change-Id: I94868250591862b376049c76bd21cb7e85f82569
Signed-off-by: Jens Rottmann <JRottmann@LiPPERTembedded.de>
Reviewed-on: http://review.coreboot.org/2831
Tested-by: build bot (Jenkins)
Reviewed-by: Ronald G. Minnich <rminnich@gmail.com>
diff --git a/src/mainboard/amd/inagua/Makefile.inc b/src/mainboard/amd/inagua/Makefile.inc
index 17443bc2..b84a03a 100644
--- a/src/mainboard/amd/inagua/Makefile.inc
+++ b/src/mainboard/amd/inagua/Makefile.inc
@@ -35,4 +35,4 @@
 ramstage-y += PlatformGnbPcie.c
 
 ramstage-y += reset.c
-
+ramstage-y += broadcom.c