drm/amd/display: move FPU code from dcn30 clk mgr to DML folder

The -mno-gnu-attribute option in clk mgr makefile for dcn30 hides a soft
vs hard fp error for powerpc. After removing this flag, we can see some
FPU code remains there:

gcc-11.3.0-nolibc/powerpc64-linux/bin/powerpc64-linux-ld:
drivers/gpu/drm/amd/amdgpu/../display/dc/dml/display_mode_lib.o uses
hard float,
drivers/gpu/drm/amd/amdgpu/../display/dc/clk_mgr/dcn30/dcn30_clk_mgr.o
uses soft float

Therefore, remove the -mno-gnu-attribute flag for dcn30/powerpc and move
FPU-associated code to DML folder.

Signed-off-by: Melissa Wen <mwen@igalia.com>
Reviewed-by: Rodrigo Siqueira <Rodrigo.Siqueira@amd.com>
Signed-off-by: Alex Deucher <alexander.deucher@amd.com>