drm/amd/display: Protect update_bw_bounding_box FPU code.

For DCN3/3.01/3.02 at least these use the fpu.

v2: squash in build fix for when DCN is not enabled (Leo)

Signed-off-by: Bas Nieuwenhuizen <bas@basnieuwenhuizen.nl>
Signed-off-by: Alex Deucher <alexander.deucher@amd.com>
Cc: stable@vger.kernel.org