drm/amd/display: Add a trace event for brightness programming

[Why]
Brightness programming may involve a conversion of a user requested
brightness against what was in a custom brightness curve. The values
might not match what a user programmed.

[How]
Add a new trace event to show specific converted brightness values.

Reviewed-by: Alex Hung <alex.hung@amd.com>
Link: https://lore.kernel.org/r/20250623171114.1156451-2-mario.limonciello@amd.com


Signed-off-by: Mario Limonciello <mario.limonciello@amd.com>
Signed-off-by: Alex Deucher <alexander.deucher@amd.com>