drm/amd/display: Add Read Histogram command header

[Why]
Read the histogram for VariBright validation

[How]
Add dc/dmub functions to read histogram and ACE

Reviewed-by: Jun Lei <jun.lei@amd.com>
Signed-off-by: Chun-Liang Chang <Chun-Liang.Chang@amd.com>
Signed-off-by: Aurabindo Pillai <aurabindo.pillai@amd.com>
Tested-by: Daniel Wheeler <daniel.wheeler@amd.com>
Signed-off-by: Alex Deucher <alexander.deucher@amd.com>