Fix vmalloc memory accounting.

VmallocUsed from meminfo sums all vmalloc'd
memory areas, but it shouldn't count the areas
that were mapped with ioremap(); ioremap()'d
ranges usually map to I/O memory, not actual
physical memory.

Binder and CMA are exceptions, but in the
common case we're more accurate not counting
those regions either.

Bug: 20483106
Change-Id: I75e74d9477a30a3de84877531b6e614a71469d24