drm/amd/display: Increase precision for bpp in DSC calculations

[Why?]
Many DSC variables and related functions use whole bits for bpp.

[How?]
Change variables and related functions to use 16ths of a bit for bpp.
Tested-by: NDaniel Wheeler <daniel.wheeler@amd.com>
Signed-off-by: NDillon Varone <dillon.varone@amd.com>
Signed-off-by: NJun Lei <jun.lei@amd.com>
Reviewed-by: NWenjing Liu <Wenjing.Liu@amd.com>
Acked-by: NSolomon Chiu <solomon.chiu@amd.com>
Signed-off-by: NAlex Deucher <alexander.deucher@amd.com>

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

@@ -770,6 +770,7 @@ struct dc_crtc_timing {
 #endif
 
 	struct dc_crtc_timing_flags flags;
+	uint32_t dsc_fixed_bits_per_pixel_x16; /* DSC target bitrate in 1/16 of bpp (e.g. 128 -> 8bpp) */
 	struct dc_dsc_config dsc_cfg;
 };