Upgrade to dlmalloc 2.8.5.

Move dlmalloc code to upstream-dlmalloc to make pulling upstream changes
easier.
Declare pvalloc and malloc_usable_size routines present in malloc.h but with
missing implementations. Remove other functions from malloc.h that have
no implementation nor use in Android.

Change-Id: Ia6472ec6cbebc9ad1ef99f4669de9d33fcc2efb4