drivers/intel/gma: Put gma_gfxinit() into its own header

The current header `i915.h` is too invasive to be used everywhere where
we want to use *libgfxinit*.

Change-Id: Iba57256d536e301e598d98182448d2daa1bf9a89
Signed-off-by: Nico Huber <nico.huber@secunet.com>
Reviewed-on: https://review.coreboot.org/20112
Tested-by: build bot (Jenkins) <no-reply@coreboot.org>
Reviewed-by: Arthur Heymans <arthur@aheymans.xyz>
diff --git a/src/northbridge/intel/haswell/gma.c b/src/northbridge/intel/haswell/gma.c
index a7b61e2..535a7f0 100644
--- a/src/northbridge/intel/haswell/gma.c
+++ b/src/northbridge/intel/haswell/gma.c
@@ -23,6 +23,7 @@
 #include <device/pci_ids.h>
 #include <drivers/intel/gma/i915_reg.h>
 #include <drivers/intel/gma/i915.h>
+#include <drivers/intel/gma/libgfxinit.h>
 #include <cpu/intel/haswell/haswell.h>
 #include <drivers/intel/gma/opregion.h>
 #include <southbridge/intel/lynxpoint/nvs.h>