drm/amd/display: Remove duplicate header

Remove custom_float.h which is included more than once

Acked-by: Souptick Joarder <jrdr.linux@gmail.com>
Signed-off-by: Brajeswar Ghosh <brajeswar.linux@gmail.com>
Signed-off-by: Alex Deucher <alexander.deucher@amd.com>