ANDROID: binder: show high watermark of alloc->pages.

Show the high watermark of the index into the alloc->pages
array, to facilitate sizing the buffer on a per-process
basis.

Signed-off-by: Martijn Coenen <maco@android.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
(cherry picked from commit 8d9a3ab6c17e9473ab31484da382914537e60152)