drm/amd/display: Don't use optimized gamma22 with eetf

[why]
Optimized gamma22 assumes fixed point distribution which is not true
for eetf true.

[how]
Use long calculation for eetf.

Signed-off-by: Aidan Yang <Aidan.Yang@amd.com>
Reviewed-by: Krunoslav Kovac <Krunoslav.Kovac@amd.com>
Acked-by: Leo Li <sunpeng.li@amd.com>
Acked-by: Reza Amini <Reza.Amini@amd.com>
Signed-off-by: Alex Deucher <alexander.deucher@amd.com>