drm/amd/display: Fix default DC and AC levels

[Why]
DC and AC levels are advertised in a percentage, not a luminance.

[How]
Scale DC and AC levels to supported values.

Closes: https://gitlab.freedesktop.org/drm/amd/-/issues/4221


Reviewed-by: Alex Hung <alex.hung@amd.com>
Signed-off-by: Mario Limonciello <mario.limonciello@amd.com>
Signed-off-by: Wayne Lin <wayne.lin@amd.com>
Tested-by: Daniel Wheeler <daniel.wheeler@amd.com>
Signed-off-by: Alex Deucher <alexander.deucher@amd.com>