drm/amd/display: Drop unnecessary FPU flags on dcn302 files

We already isolated the DCN302 code in the DML folder, but we forgot to
drop the FPU flags from the Makefile. This commit drops those flags.

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