drm/amdgpu/display: properly guard dc_dsc_stream_bandwidth_in_kbps

Move the function protoype to the right header and guard
the call with CONFIG_DRM_AMD_DC_DCN as DSC is only available
with DCN.

Fixes: 8c2f14c3 ("drm/amd/display: Add changes for dsc bpp in 16ths and unify bw calculations")
Reviewed-by: Harry Wentland <harry.wentland@amd.com>
Signed-off-by: Alex Deucher <alexander.deucher@amd.com>
Cc: Dillon Varone <dillon.varone@amd.com>
Cc: Stephen Rothwell <sfr@canb.auug.org.au>

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

@@ -3498,17 +3498,17 @@ void dc_link_enable_hpd_filter(struct dc_link *link, bool enable)
 	}
 }
 
-uint32_t dc_dsc_stream_bandwidth_in_kbps(uint32_t pix_clk_100hz, uint32_t bpp_x16);
-
 uint32_t dc_bandwidth_in_kbps_from_timing(
 	const struct dc_crtc_timing *timing)
 {
 	uint32_t bits_per_channel = 0;
 	uint32_t kbps;
 
+#if defined(CONFIG_DRM_AMD_DC_DCN)
 	if (timing->flags.DSC) {
 		return dc_dsc_stream_bandwidth_in_kbps(timing->pix_clk_100hz, timing->dsc_cfg.bits_per_pixel);
 	}
+#endif
 
 	switch (timing->display_color_depth) {
 	case COLOR_DEPTH_666:

drivers/gpu/drm/amd/display/dc/dc_dsc.h

@@ -88,4 +88,6 @@ void dc_dsc_policy_set_max_target_bpp_limit(uint32_t limit);
 
 void dc_dsc_policy_set_enable_dsc_when_not_needed(bool enable);
 
+uint32_t dc_dsc_stream_bandwidth_in_kbps(uint32_t pix_clk_100hz, uint32_t bpp_x16);
+
 #endif