ANDROID: add ion_stat tracepoint to common kernel

Emitted an event whenever ion buffers are created or freed.
This enables tracking ion memory utilization changes, as well as
individual buffer allocations.

This was inspired by the pixel kernel patches by timmurray@ and
carmenjackson@.

Test: manual test on cuttlefish
Bug: 154302786
Change-Id: I4d4b23ae4dbda5012d3582f5564a87e0d08c68c7
Signed-off-by: Ioannis Ilkos <ilkos@google.com>