Set up 3rdparty/libgfxinit

`libgfxinit` is a SPARK library for graphics modesetting. It supports
Intel integrated graphics only, strictly speaking, the Core i processor
line.

Change-Id: Idf4b0e5fbf37a5d974075b2e44d1fa16dc428da3
Signed-off-by: Nico Huber <nico.huber@secunet.com>
Reviewed-on: https://review.coreboot.org/16949
Tested-by: build bot (Jenkins)
Reviewed-by: Stefan Reinauer <stefan.reinauer@coreboot.org>
diff --git a/.gitmodules b/.gitmodules
index c545ccd..c3270e6 100644
--- a/.gitmodules
+++ b/.gitmodules
@@ -18,3 +18,6 @@
 [submodule "libhwbase"]
 	path = 3rdparty/libhwbase
 	url = ../libhwbase.git
+[submodule "libgfxinit"]
+	path = 3rdparty/libgfxinit
+	url = ../libgfxinit.git