drm/amd/display: Add Logging for Gamma Related information

[Why]
A recent bug showed that logging would be useful in debugging
various gamma issues.

[How]
Fix formatting for easier graphing.
Prevent performance hit when doing diag.

Signed-off-by: Wyatt Wood <wyatt.wood@amd.com>
Reviewed-by: Aric Cyr <Aric.Cyr@amd.com>
Acked-by: Bhawanpreet Lakha <Bhawanpreet.Lakha@amd.com>
Signed-off-by: Alex Deucher <alexander.deucher@amd.com>