soc/intel/gma: Implement fsp_soc_get_igd_bar() in common code

`fsp/util.h` draws incompatible UDK headers in. Hence, we have to
declare it locally again.

Change-Id: Iaa5981088eeb5c36f765d6332ae47a38a6a4c875
Signed-off-by: Nico Huber <nico.h@gmx.de>
Reviewed-on: https://review.coreboot.org/c/coreboot/+/40729
Reviewed-by: Angel Pons <th3fanbus@gmail.com>
Tested-by: build bot (Jenkins) <no-reply@coreboot.org>

src/soc/intel/skylake/graphics.c

@@ -10,11 +10,6 @@
 #include <soc/ramstage.h>
 #include <types.h>
 
-uintptr_t fsp_soc_get_igd_bar(void)
-{
-	return graphics_get_memory_base();
-}
-
 void graphics_soc_init(struct device *dev)
 {
 	struct soc_intel_skylake_config *conf = config_of(dev);