drm/amd/display: Use SDR white level to calculate matrix coefficients

[WHY]
Certain profiles have higher HDR multiplier than SDR white level max
which is not currently supported.

[HOW]
Use SDR white level when calculating matrix coefficients for HDR RGB MPO
path instead of HDR multiplier.

Cc: Mario Limonciello <mario.limonciello@amd.com>
Cc: Alex Deucher <alexander.deucher@amd.com>
Cc: stable@vger.kernel.org
Reviewed-by: Jun Lei <jun.lei@amd.com>
Signed-off-by: Samson Tam <Samson.Tam@amd.com>
Signed-off-by: Alex Hung <alex.hung@amd.com>
Tested-by: Daniel Wheeler <daniel.wheeler@amd.com>
Signed-off-by: Alex Deucher <alexander.deucher@amd.com>