Reorganize initmem_init() such that,

* Different NUMA init methods are iterated in a consistent way.

* Each iteration re-initializes all the parameters and different
  method can be tried after a failure.

* Dummy init is handled the same as other methods.

Apart from how retry after failure, this patch doesn't change the
behavior.  The call sequences are kept equivalent across the
conversion.

After the change, bad_srat() doesn't need to clear apic to node
mapping or worry about numa_off.  Simplified accordingly.
Signed-off-by: Tejun Heo <tj@kernel.org>
Cc: Yinghai Lu <yinghai@kernel.org>
Cc: Brian Gerst <brgerst@gmail.com>
Cc: Cyrill Gorcunov <gorcunov@gmail.com>
Cc: Shaohui Zheng <shaohui.zheng@intel.com>
Cc: David Rientjes <rientjes@google.com>
Cc: Ingo Molnar <mingo@elte.hu>
Cc: H. Peter Anvin <hpa@linux.intel.com>