ANDROID: Track per-process dmabuf RSS HWM

A per-process high watermark counter for dmabuf memory is useful for
detecting bursty / transient allocations causing memory pressure spikes
that don't appear in the dmabuf RSS counter when userspace reacts to
memory pressure and reads RSS after buffers have already been freed.

The /proc/<pid>/dmabuf_rss_hwm file in procfs now reports the maximum
value of /proc/<pid>/dmabuf_rss during the lifetime of the process.

The value of /proc/<pid>/dmabuf_rss_hwm can be reset to the current
value of /proc/<pid>/dmabuf_rss by writing "0" to the file.

Bug: 424648392
Change-Id: I1260ccc91601e1976f3e60ec3aa89e53281f17eb
Signed-off-by: T.J. Mercier <tjmercier@google.com>