drm/amd/display: Remove FPU flags from DCN30 Makefile

At this stage, we must have all the FPU code for DCN30 isolated in the
DML folder. Drop FPU flags from Makefile.

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>