drm/amd/display: Fix timing bandwidth calculation for HDMI

drm/amd/display: Fix timing bandwidth calculation for HDMI

[Why && How]
The current bandwidth calculation for timing doesn't account for
certain HDMI modes overhead which leads to DSC can't be enabled.
Add support to calculate the actual bandwidth for these HDMI modes.

Reviewed-by: Chris Park <chris.park@amd.com>
Acked-by: Roman Li <roman.li@amd.com>
Signed-off-by: Leo (Hanghong) Ma <hanghong.ma@amd.com>
Tested-by: Daniel Wheeler <daniel.wheeler@amd.com>
Signed-off-by: Alex Deucher <alexander.deucher@amd.com>