drm/amd/display: Fix 10bit 4K display on CIK GPUs

Commit 72a7cf0a ("drm/amd/display: Keep linebuffer pixel depth at
30bpp for DCE-11.0.") doesn't seems to have fixed 10bit 4K rendering over
DisplayPort for CIK GPUs. On my machine with a HAWAII GPU I get a broken
image that looks like it has an effective resolution of 1920x1080 but
scaled up in an irregular way. Reverting the commit or applying this
patch fixes the problem on v5.14-rc1.

Fixes: 72a7cf0a

 ("drm/amd/display: Keep linebuffer pixel depth at 30bpp for DCE-11.0.")
Acked-by: Mario Kleiner <mario.kleiner.de@gmail.com>
Reviewed-by: Harry Wentland <harry.wentland@amd.com>
Signed-off-by: Liviu Dudau <liviu@dudau.co.uk>
Signed-off-by: Alex Deucher <alexander.deucher@amd.com>