drm/amd/display: fix soft-fp vs hard-fp on DCN 3.1 family for powerpc

Move remaining FPU code to DML folder that caused compilation error for
powerpc. This patch depends on [1] to prevent the error below:

/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/dcn31/dcn31_resource.o uses soft float
/gcc-11.3.0-nolibc/powerpc64-linux/bin/powerpc64-linux-ld: failed to merge target specific data of file drivers/gpu/drm/amd/amdgpu/../display/dc/dcn31/dcn31_resource.o
/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/dcn315/dcn315_resource.o uses soft float
/gcc-11.3.0-nolibc/powerpc64-linux/bin/powerpc64-linux-ld: failed to merge target specific data of file drivers/gpu/drm/amd/amdgpu/../display/dc/dcn315/dcn315_resource.o
/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/dcn316/dcn316_resource.o uses soft float
/gcc-11.3.0-nolibc/powerpc64-linux/bin/powerpc64-linux-ld: failed to merge target specific data of file drivers/gpu/drm/amd/amdgpu/../display/dc/dcn316/dcn316_resource.o

[1] https://lore.kernel.org/amd-gfx/20220716195144.342960-1-mwen@igalia.com/

Reported-by: Guenter Roeck <linux@roeck-us.net>
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>