mm,x86: fix kmap_atomic_push vs ioremap_32.c

It appears i386 uses kmap_atomic infrastructure regardless of
CONFIG_HIGHMEM which results in a compile error when highmem is disabled.

Cure this by providing the needed few bits for both CONFIG_HIGHMEM and
CONFIG_X86_32.

Signed-off-by: Peter Zijlstra <a.p.zijlstra@chello.nl>
Reported-by: Chris Wilson <chris@chris-wilson.co.uk>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>