The placement is something TTM/BO internal and the RAS code should
avoid touching that directly.

Add a helper to create a BO at a fixed location and use that instead.

v2: squash in fixes (Alex)
Signed-off-by: NChristian König <christian.koenig@amd.com>
Reviewed-by: NGuchun Chen <guchun.chen@amd.com>
Reviewed-by: NAlex Deucher <alexander.deucher@amd.com>
Signed-off-by: NAlex Deucher <alexander.deucher@amd.com>