gpu: ion: Add better debugfs information

In debugfs, clients now show individual allocations.
Carveout heaps now give the number of bytes currently
allocated out of total possible bytes. The system heaps
just show the number of bytes currently allocated.

Change-Id: I4acfcdc1089c73c28041e09cb6b5a03b956e936a
Signed-off-by: Laura Abbott <lauraa@codeaurora.org>