drm/radeon: mark symbols static where possible

We get 4 warnings when building kernel with W=1:
drivers/gpu/drm/radeon/si.c:7850:5: warning: no previous prototype for 'si_vce_send_vcepll_ctlreq' [-Wmissing-prototypes]
drivers/gpu/drm/radeon/radeon_dp_mst.c:226:21: warning: no previous prototype for 'radeon_mst_best_encoder' [-Wmissing-prototypes]
drivers/gpu/drm/radeon/radeon_dp_mst.c:344:26: warning: no previous prototype for 'radeon_mst_find_connector' [-Wmissing-prototypes]
drivers/gpu/drm/radeon/radeon_dp_mst.c:600:6: warning: no previous prototype for 'radeon_dp_mst_encoder_destroy' [-Wmissing-prototypes]

In fact, these functions are only used in the file in which they are
declared and don't need a declaration, but can be made static.
So this patch marks these functions with 'static'.
Reviewed-by: Christian König <christian.koenig@amd.com>
Signed-off-by: Baoyou Xie <baoyou.xie@linaro.org>
Signed-off-by: Alex Deucher <alexander.deucher@amd.com>

drivers/gpu/drm/radeon/radeon_dp_mst.c

@@ -223,7 +223,8 @@ radeon_dp_mst_mode_valid(struct drm_connector *connector,
 	return MODE_OK;
 }
 
-struct drm_encoder *radeon_mst_best_encoder(struct drm_connector *connector)
+static struct
+drm_encoder *radeon_mst_best_encoder(struct drm_connector *connector)
 {
 	struct radeon_connector *radeon_connector = to_radeon_connector(connector);
 
@@ -341,7 +342,8 @@ const struct drm_dp_mst_topology_cbs mst_cbs = {
 	.hotplug = radeon_dp_mst_hotplug,
 };
 
-struct radeon_connector *radeon_mst_find_connector(struct drm_encoder *encoder)
+static struct
+radeon_connector *radeon_mst_find_connector(struct drm_encoder *encoder)
 {
 	struct drm_device *dev = encoder->dev;
 	struct drm_connector *connector;
@@ -597,7 +599,7 @@ static const struct drm_encoder_helper_funcs radeon_mst_helper_funcs = {
 	.commit = radeon_mst_encoder_commit,
 };
 
-void radeon_dp_mst_encoder_destroy(struct drm_encoder *encoder)
+static void radeon_dp_mst_encoder_destroy(struct drm_encoder *encoder)
 {
 	drm_encoder_cleanup(encoder);
 	kfree(encoder);

drivers/gpu/drm/radeon/si.c

@@ -7858,7 +7858,7 @@ static void si_program_aspm(struct radeon_device *rdev)
 	}
 }
 
-int si_vce_send_vcepll_ctlreq(struct radeon_device *rdev)
+static int si_vce_send_vcepll_ctlreq(struct radeon_device *rdev)
 {
 	unsigned i;