drm/radeon/radeon_legacy_encoders: Move 'radeon_add_legacy_encoder's prototype to shared location

Fixes the following W=1 kernel build warning(s):

 drivers/gpu/drm/radeon/radeon_legacy_encoders.c:1746:1: warning: no previous prototype for ‘radeon_add_legacy_encoder’ [-Wmissing-prototypes]
 1746 | radeon_add_legacy_encoder(struct drm_device *dev, uint32_t encoder_enum, uint32_t supported_device)
 | ^~~~~~~~~~~~~~~~~~~~~~~~~

Cc: Alex Deucher <alexander.deucher@amd.com>
Cc: "Christian König" <christian.koenig@amd.com>
Cc: David Airlie <airlied@linux.ie>
Cc: Daniel Vetter <daniel@ffwll.ch>
Cc: Sumit Semwal <sumit.semwal@linaro.org>
Cc: amd-gfx@lists.freedesktop.org
Cc: dri-devel@lists.freedesktop.org
Cc: linux-media@vger.kernel.org
Cc: linaro-mm-sig@lists.linaro.org
Signed-off-by: Lee Jones <lee.jones@linaro.org>
Signed-off-by: Alex Deucher <alexander.deucher@amd.com>

drivers/gpu/drm/radeon/radeon_atombios.c

@@ -35,16 +35,12 @@
 #include "atom-bits.h"
 #include "radeon_asic.h"
 #include "radeon_atombios.h"
+#include "radeon_legacy_encoders.h"
 
 extern void
 radeon_add_atom_encoder(struct drm_device *dev, uint32_t encoder_enum,
 			uint32_t supported_device, u16 caps);
 
-/* from radeon_legacy_encoder.c */
-extern void
-radeon_add_legacy_encoder(struct drm_device *dev, uint32_t encoder_enum,
-			  uint32_t supported_device);
-
 union atom_supported_devices {
 	struct _ATOM_SUPPORTED_DEVICES_INFO info;
 	struct _ATOM_SUPPORTED_DEVICES_INFO_2 info_2;

drivers/gpu/drm/radeon/radeon_combios.c

@@ -31,6 +31,7 @@
 #include <drm/radeon_drm.h>
 
 #include "radeon.h"
+#include "radeon_legacy_encoders.h"
 #include "atom.h"
 
 #ifdef CONFIG_PPC_PMAC
@@ -40,11 +41,6 @@
 #include <asm/prom.h>
 #endif /* CONFIG_PPC_PMAC */
 
-/* from radeon_legacy_encoder.c */
-extern void
-radeon_add_legacy_encoder(struct drm_device *dev, uint32_t encoder_enum,
-			  uint32_t supported_device);
-
 /* old legacy ATI BIOS routines */
 
 /* COMBIOS table offsets */

drivers/gpu/drm/radeon/radeon_legacy_encoders.h

@@ -30,5 +30,7 @@
 
 void radeon_legacy_backlight_init(struct radeon_encoder *radeon_encoder,
 				  struct drm_connector *drm_connector);
+void radeon_add_legacy_encoder(struct drm_device *dev, uint32_t encoder_enum,
+			       uint32_t supported_device);
 
 #endif				/* __RADEON_LEGACY_ENCODERS_H__ */