drm/amdgpu: add helper function to init asd ucode

asd is unified ucode across asic. it is not necessary
to keep its software structure to be ip specific one

Signed-off-by: Hawking Zhang <Hawking.Zhang@amd.com>
Reviewed-by: Guchun Chen <guchun.chen@amd.com>
Reviewed-by: John Clements <john.clements@amd.com>
Signed-off-by: Alex Deucher <alexander.deucher@amd.com>