sh: Prefer slab_is_available() over after_bootmem.

This kills off after_bootmem and switches to using slab_is_available()
instead. Presently the only place this is used is by the sh64 ioremap,
and there's not much point in keeping the reference around otherwise.

Signed-off-by: Paul Mundt <lethal@linux-sh.org>

diff --cc arch/sh/mm/init.c
Simple merge

diff --cc arch/sh/mm/ioremap_64.c
Simple merge