drm/amd/display: Move populate phaton function to dml

The function dcn32_helper_populate_phantom_dlg_params uses FPU
operations. For this reason, this commit moves this function to the
dcn32_fpu file, and we ensure that we only invoke it under the
kernel_fpu protection.

Tested-by: Daniel Wheeler <daniel.wheeler@amd.com>
Reviewed-by: Harry Wentland <Harry.Wentland@amd.com>
Signed-off-by: Rodrigo Siqueira <Rodrigo.Siqueira@amd.com>
Signed-off-by: Alex Deucher <alexander.deucher@amd.com>