drm/amd/display: Drop FPU code from dcn321 resource

This commit fully move the missing FPU operations from dcn321 resource
to dcn321 fpu. It also remove those FPU flags from the Makefile.

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>