drm/amd/display: Add support for custom brightness curve

drm/amd/display: Add support for custom brightness curve

Some systems specify in the firmware a brightness curve that better
reflects the characteristics of the panel used. This is done in the
form of data points and matching luminance percentage.

When converting a userspace requested brightness value use that curve
to convert to a firmware intended brightness value.

Reviewed-by: Alex Hung <alex.hung@amd.com>
Link: https://lore.kernel.org/r/20250228185145.186319-5-mario.limonciello@amd.com
Signed-off-by: Mario Limonciello <mario.limonciello@amd.com>
Signed-off-by: Alex Deucher <alexander.deucher@amd.com>