mmap.c: deinline a few functions

__vma_link_file and expand_downwards functions are not small, yeat they
are marked inline.  They probably had one callsite sometime in the past,
but now they have more.  In order to prevent similar thing, I also
deinlined expand_upwards, despite it having only pne callsite.  Nowadays
gcc auto-inlines such static functions anyway.  In find_extend_vma, I
removed one extra level of indirection.

Patch is deliberately generated with -U $BIGNUM to make
it easier to see that functions are big.

Result:

# size */*/mmap.o */vmlinux
   text    data     bss     dec     hex filename
   9514     188      16    9718    25f6 0.org/mm/mmap.o
   9237     188      16    9441    24e1 deinline/mm/mmap.o
6124402  858996  389480 7372878  70804e 0.org/vmlinux
6124113  858996  389480 7372589  707f2d deinline/vmlinux

Signed-off-by: Denys Vlasenko <vda.linux@googlemail.com>
Cc: Hugh Dickins <hugh@veritas.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>