task_vsize() doesn't need mm->mmap_sem for the CONFIG_MMU case; the
semaphore doesn't prevent mm->total_vm from going stale or getting
inconsistent with other numbers regardless.  Also, KSTK_EIP() and
KSTK_ESP() don't want or need protection from mm->mmap_sem either.  So this
pushes mm->mmap_sem to task_vsize() in the CONFIG_MMU=n task_vsize().

Also, hoist the prototype of task_vsize() into proc_fs.h

The net result of this is a small speedup of procps for CONFIG_MMU.
Signed-off-by: Andrew Morton <akpm@osdl.org>
Signed-off-by: Linus Torvalds <torvalds@osdl.org>