x86: ifdef 32-bit and 64-bit NR_RANGE_MR for save_mr() unification

Impact: cleanup

As a trivial preparation for moving common code to arc/x86/mm/init.c,
ifdef the 32-bit and 64-bit versions of NR_RANGE_MR.

Signed-off-by: Pekka Enberg <penberg@cs.helsinki.fi>
Cc: Yinghai Lu <yinghai@kernel.org>
LKML-Reference: <1236257708-27269-12-git-send-email-penberg@cs.helsinki.fi>
Signed-off-by: Ingo Molnar <mingo@elte.hu>