drm/amd/display: Call FP Protect Before Mode Programming/Mode Support

[Why]
Memory allocation occurs within dml21_validate() for adding phantom planes.
May cause kernel to be tainted due to usage of FP Start.

[How]
Move FP start from dml21_validate to before mode programming/mode support.
Calculations requiring floating point are all done within mode programming
or mode support.

Reviewed-by: Alvin Lee <alvin.lee2@amd.com>
Signed-off-by: Austin Zheng <Austin.Zheng@amd.com>
Signed-off-by: Ray Wu <ray.wu@amd.com>
Tested-by: Daniel Wheeler <daniel.wheeler@amd.com>
Signed-off-by: Alex Deucher <alexander.deucher@amd.com>
(cherry picked from commit fe3250f1)