drm/amd/display/dc/core/dc_resource: Staticify local functions

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

 drivers/gpu/drm/amd/amdgpu/../display/dc/core/dc_resource.c:1120:5: warning: no previous prototype for ‘shift_border_left_to_dst’ [-Wmissing-prototypes]
 drivers/gpu/drm/amd/amdgpu/../display/dc/core/dc_resource.c:1131:6: warning: no previous prototype for ‘restore_border_left_from_dst’ [-Wmissing-prototypes]

Cc: Harry Wentland <harry.wentland@amd.com>
Cc: Leo Li <sunpeng.li@amd.com>
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: amd-gfx@lists.freedesktop.org
Cc: dri-devel@lists.freedesktop.org
Signed-off-by: Lee Jones <lee.jones@linaro.org>
Signed-off-by: Alex Deucher <alexander.deucher@amd.com>

drivers/gpu/drm/amd/display/dc/core/dc_resource.c

@@ -1117,7 +1117,7 @@ static void calculate_inits_and_adj_vp(struct pipe_ctx *pipe_ctx)
  * We also need to make sure pipe_ctx->plane_res.scl_data.h_active uses the
  * original h_border_left value in its calculation.
  */
-int shift_border_left_to_dst(struct pipe_ctx *pipe_ctx)
+static int shift_border_left_to_dst(struct pipe_ctx *pipe_ctx)
 {
 	int store_h_border_left = pipe_ctx->stream->timing.h_border_left;
 
@@ -1128,8 +1128,8 @@ int shift_border_left_to_dst(struct pipe_ctx *pipe_ctx)
 	return store_h_border_left;
 }
 
-void restore_border_left_from_dst(struct pipe_ctx *pipe_ctx,
-                                  int store_h_border_left)
+static void restore_border_left_from_dst(struct pipe_ctx *pipe_ctx,
+					 int store_h_border_left)
 {
 	pipe_ctx->stream->dst.x -= store_h_border_left;
 	pipe_ctx->stream->timing.h_border_left = store_h_border_left;