VM: add "vm_brk()" helper function

It does the same thing as "do_brk()", except it handles the VM locking
too.

It turns out that all external callers want that anyway, so we can make
do_brk() static to just mm/mmap.c while at it.

Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
diff --git a/mm/nommu.c b/mm/nommu.c
index f59e170..6341933 100644
--- a/mm/nommu.c
+++ b/mm/nommu.c
@@ -1744,7 +1744,7 @@
 	kleave("");
 }
 
-unsigned long do_brk(unsigned long addr, unsigned long len)
+unsigned long vm_brk(unsigned long addr, unsigned long len)
 {
 	return -ENOMEM;
 }