drm/radeon: Move prototypes to shared header

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

 drivers/gpu/drm/radeon/radeon_kms.c:756:5: warning: no previous prototype for ‘radeon_get_vblank_counter_kms’ [-Wmissing-prototypes]
 756 | u32 radeon_get_vblank_counter_kms(struct drm_crtc *crtc)
 | ^~~~~~~~~~~~~~~~~~~~~~~~~~~~~
 drivers/gpu/drm/radeon/radeon_kms.c:826:5: warning: no previous prototype for ‘radeon_enable_vblank_kms’ [-Wmissing-prototypes]
 826 | int radeon_enable_vblank_kms(struct drm_crtc *crtc)
 | ^~~~~~~~~~~~~~~~~~~~~~~~
 drivers/gpu/drm/radeon/radeon_kms.c:853:6: warning: no previous prototype for ‘radeon_disable_vblank_kms’ [-Wmissing-prototypes]
 853 | void radeon_disable_vblank_kms(struct drm_crtc *crtc)
 | ^~~~~~~~~~~~~~~~~~~~~~~~~

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.h

@@ -2832,6 +2832,12 @@ extern void radeon_program_register_sequence(struct radeon_device *rdev,
 					     const u32 array_size);
 struct radeon_device *radeon_get_rdev(struct ttm_bo_device *bdev);
 
+/* KMS */
+
+u32 radeon_get_vblank_counter_kms(struct drm_crtc *crtc);
+int radeon_enable_vblank_kms(struct drm_crtc *crtc);
+void radeon_disable_vblank_kms(struct drm_crtc *crtc);
+
 /*
  * vm
  */

drivers/gpu/drm/radeon/radeon_display.c

@@ -45,10 +45,6 @@
 #include "atom.h"
 #include "radeon.h"
 
-u32 radeon_get_vblank_counter_kms(struct drm_crtc *crtc);
-int radeon_enable_vblank_kms(struct drm_crtc *crtc);
-void radeon_disable_vblank_kms(struct drm_crtc *crtc);
-
 static void avivo_crtc_load_lut(struct drm_crtc *crtc)
 {
 	struct radeon_crtc *radeon_crtc = to_radeon_crtc(crtc);