drm/amdgpu: fix calltrace during kmd unload(v3)

issue:
kernel would report a warning from a double unpin
during the driver unloading on the CSB bo

why:
we unpin it during hw_fini, and there will be another
unpin in sw_fini on CSB bo.

fix:
actually we don't need to pin/unpin it during
hw_init/fini since it is created with kernel pinned,
we only need to fullfill the CSB again during hw_init
to prevent CSB/VRAM lost after S3

v2:
get_csb in init_rlc so hw_init() will make CSIB content
back even after reset or s3

v3:
use bo_create_kernel instead of bo_create_reserved for CSB
otherwise the bo_free_kernel() on CSB is not aligned and
would lead to its internal reserve pending there forever

take care of gfx7/8 as well

Signed-off-by: Monk Liu <Monk.Liu@amd.com>
Reviewed-by: Hawking Zhang <Hawking.Zhang@amd.com>
Reviewed-by: Xiaojie Yuan <xiaojie.yuan@amd.com>
Signed-off-by: Alex Deucher <alexander.deucher@amd.com>