drm/amd/display: add dc_fixpt_from_s3132 helper

Detach value translation from CTM to reuse it for programming HDR
multiplier property.

Reviewed-by: Harry Wentland <harry.wentland@amd.com>
Signed-off-by: Joshua Ashton <joshua@froggi.es>
Signed-off-by: Melissa Wen <mwen@igalia.com>
Signed-off-by: Alex Deucher <alexander.deucher@amd.com>