drm/amdgpu: parameterize ttm BO destroy callback

Make provision to pass different ttm BO destroy callback
while creating a amdgpu_bo.

Signed-off-by: Nirmoy Das <nirmoy.das@amd.com>
Reviewed-by: Christian König <christian.koenig@amd.com>
Signed-off-by: Alex Deucher <alexander.deucher@amd.com>