3rdparty/libgfxinit: Update submodule pointer

Update to current master. Beside a minor workaround for GCC 8
compatibility, this includes only refactorings and preparations
for G4x support.

Change-Id: I6b2aa6bd9d41b852dacd8e1dfe89d92c8a548121
Signed-off-by: Nico Huber <nico.h@gmx.de>
Reviewed-on: https://review.coreboot.org/26420
Reviewed-by: Patrick Georgi <pgeorgi@google.com>
Reviewed-by: Angel Pons <th3fanbus@gmail.com>
Reviewed-by: Arthur Heymans <arthur@aheymans.xyz>
Tested-by: build bot (Jenkins) <no-reply@coreboot.org>

3rdparty/libgfxinit

@@ -1 +1 @@
-Subproject commit 7628493a7e7acaba93d607db008a59ec8fa8eebe
+Subproject commit 98a673dc57d90cc79e64c53bd02cfcc1c48ea1aa