coccinelle: api: add vma_pages.cocci

This semantic patch replaces explicit computations of vma page count
with explicit function call.

Signed-off-by: Dmitry Kalinkin <dmitry.kalinkin@gmail.com>
Acked-by: Julia Lawall <julia.lawall@lip6.fr>
Signed-off-by: Michal Marek <mmarek@suse.cz>