drm/amd/display: make some functions static

These functions are not used outside the file dcn32_hubbub.c, so the
modification is defined as static.

drivers/gpu/drm/amd/amdgpu/../display/dc/dcn314/dcn314_dccg.c:223:6: warning: no previous prototype for ‘dccg314_set_valid_pixel_rate’.
drivers/gpu/drm/amd/amdgpu/../display/dc/dcn314/dcn314_dccg.c:184:6: warning: no previous prototype for ‘dccg314_set_dpstreamclk’.
drivers/gpu/drm/amd/amdgpu/../display/dc/dcn314/dcn314_dccg.c:140:6: warning: no previous prototype for ‘dccg314_set_dtbclk_dto’.

Link: https://bugzilla.openanolis.cn/show_bug.cgi?id=2144Reported-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/dcn314/dcn314_dccg.c

@@ -137,7 +137,7 @@ static void dccg314_set_dtbclk_p_src(
 }
 
 /* Controls the generation of pixel valid for OTG in (OTG -> HPO case) */
-void dccg314_set_dtbclk_dto(
+static void dccg314_set_dtbclk_dto(
 		struct dccg *dccg,
 		const struct dtbclk_dto_params *params)
 {
@@ -181,7 +181,7 @@ void dccg314_set_dtbclk_dto(
 	}
 }
 
-void dccg314_set_dpstreamclk(
+static void dccg314_set_dpstreamclk(
 		struct dccg *dccg,
 		enum streamclk_source src,
 		int otg_inst,
@@ -220,7 +220,7 @@ void dccg314_set_dpstreamclk(
 	}
 }
 
-void dccg314_set_valid_pixel_rate(
+static void dccg314_set_valid_pixel_rate(
 		struct dccg *dccg,
 		int ref_dtbclk_khz,
 		int otg_inst,