malloc: Annotate allocator for valgrind

This annotates malloc and friends so that valgrind can track the heap. To
do this, we need to follow a few rules:

* Call VALGRIND_MALLOCLIKE_BLOCK whenever we malloc something
* Call VALGRIND_FREELIKE_BLOCK whenever we free something (generally after
  we have done our bookkeeping)
* Call VALGRIND_RESIZEINPLACE_BLOCK whenever we change the size of an
  allocation. We don't record the original request size of a block, and
  neither does valgrind. For this reason, we pretend that the old size of
  the allocation was for 0 bytes. This marks the whole allocaton as
  undefined, so in order to mark all bits correctly, we must make the whole
  new allocation defined with VALGRIND_MAKE_MEM_DEFINED. This may cause us
  to miss some invalid reads, but there is no way to detect these without
  recording the original size of the allocation.

In addition to the above, dlmalloc itself tends to make a lot of accesses
which we know are safe, but which would be unsafe outside of dlmalloc. For
this reason, we provide a suppression file which ignores errors ocurring in
dlmalloc.c

Signed-off-by: Sean Anderson <seanga2@gmail.com>
Reviewed-by: Simon Glass <sjg@chromium.org>

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