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>

src/drivers/intel/gma/i915.h

@@ -107,7 +107,4 @@ void
 generate_fake_intel_oprom(const struct i915_gpu_controller_info *conf,
 			  struct device *dev, const char *idstr);
 
-/* interface to libgfxinit (gma.adb) */
-void gma_gfxinit(u64 mmio_base, u64 linear_fb, u32 phys_fb, int *success);
-
 #endif

src/drivers/intel/gma/libgfxinit.h

@@ -0,0 +1,19 @@
+/*
+ * This file is part of the coreboot project.
+ *
+ * This program is free software; you can redistribute it and/or modify
+ * it under the terms of the GNU General Public License as published by
+ * the Free Software Foundation; version 2 of the License.
+ *
+ * This program is distributed in the hope that it will be useful,
+ * but WITHOUT ANY WARRANTY; without even the implied warranty of
+ * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
+ * GNU General Public License for more details.
+ */
+
+#ifndef DRIVERS_INTEL_GMA_LIBGFXINIT_H
+#define DRIVERS_INTEL_GMA_LIBGFXINIT_H
+
+void gma_gfxinit(u64 mmio_base, u64 linear_fb, u32 phys_fb, int *success);
+
+#endif