mm, sl[aou]b: Common definition for boot state of the slab allocators

All allocators have some sort of support for the bootstrap status.

Setup a common definition for the boot states and make all slab
allocators use that definition.

Reviewed-by: Glauber Costa <glommer@parallels.com>
Reviewed-by: Joonsoo Kim <js1304@gmail.com>
Signed-off-by: Christoph Lameter <cl@linux.com>
Signed-off-by: Pekka Enberg <penberg@kernel.org>

Conflicts:
	mm/slab.c

Change-Id: I70396580837b3e6301babbac167622d11a808d7a