Add Kconfig options to handle the blobs repository

One option to allow using the repo (defaults to no),
one to let boards state that they require it in the
current configuration.

The build system checks out the repo if allowed, and
fails if the repo is requested by the configuration
but not desired by the user.

Change-Id: If71d80b329cf528aa467fcb0b4d9d7c7434aab27
Signed-off-by: Patrick Georgi <patrick@georgi-clan.de>
Reviewed-on: http://review.coreboot.org/957
Reviewed-by: Stefan Reinauer <stefan.reinauer@coreboot.org>
Tested-by: build bot (Jenkins)

Makefile.inc

@@ -67,6 +67,14 @@ ifeq ($(CONFIG_TRACE),y)
 ramstage-c-ccopts:= -finstrument-functions
 endif
 
+ifeq ($(CONFIG_USE_BLOBS),y)
+forgetthis:=$(shell git submodule update --init --checkout 3rdparty)
+else
+ifeq ($(CONFIG_REQUIRES_BLOB),y)
+$(error Your current configuration requires binary-only components, but you did not choose to use them)
+endif
+endif
+
 smm-c-ccopts:=-D__SMM__
 smm-S-ccopts:=-D__SMM__