drm/amdgpu: Split amdgpu_ucode_init/fini_bo into two functions

1. one is for create/free bo when init/fini
2. one is for fill the bo before fw loading

the ucode bo only need to be created when load driver
and free when driver unload.

when resume/reset, driver only need to re-fill the bo
if the bo is allocated in vram.

Suggested by Christian.

v2: Return error when bo create failed.

Reviewed-by: Alex Deucher <alexander.deucher@amd.com>
Signed-off-by: Rex Zhu <Rex.Zhu@amd.com>
Signed-off-by: Alex Deucher <alexander.deucher@amd.com>