drm/amd/display: make some functions static

These functions are not used outside the file dcn30_resource.c, so the
modification is defined as static.

drivers/gpu/drm/amd/amdgpu/../display/dc/dcn30/dcn30_resource.c:1949:6: warning: no previous prototype for ‘is_refresh_rate_support_mclk_switch_using_fw_based_vblank_stretch’.
drivers/gpu/drm/amd/amdgpu/../display/dc/dcn30/dcn30_resource.c:1919:5: warning: no previous prototype for ‘get_frame_rate_at_max_stretch_100hz’.

Link: https://bugzilla.openanolis.cn/show_bug.cgi?id=2143Reported-by: Abaci Robot <abaci@linux.alibaba.com>
Signed-off-by: Jiapeng Chong <jiapeng.chong@linux.alibaba.com>
Signed-off-by: Alex Deucher <alexander.deucher@amd.com>

drivers/gpu/drm/amd/display/dc/dcn30/dcn30_resource.c

@@ -1916,7 +1916,7 @@ static int get_refresh_rate(struct dc_state *context)
  */
 #define V_SCALE (10000 / MAX_STRETCHED_V_BLANK)
 
-int get_frame_rate_at_max_stretch_100hz(struct dc_state *context)
+static int get_frame_rate_at_max_stretch_100hz(struct dc_state *context)
 {
 	struct dc_crtc_timing *timing = NULL;
 	uint32_t sec_per_100_lines;
@@ -1946,7 +1946,7 @@ int get_frame_rate_at_max_stretch_100hz(struct dc_state *context)
 	return scaled_refresh_rate;
 }
 
-bool is_refresh_rate_support_mclk_switch_using_fw_based_vblank_stretch(struct dc_state *context)
+static bool is_refresh_rate_support_mclk_switch_using_fw_based_vblank_stretch(struct dc_state *context)
 {
 	int refresh_rate_max_stretch_100hz;
 	int min_refresh_100hz;