staging: android: ion: add ftrace logging for cache maintenance

Trace when ION applies, and when it skips, cache maintenance.

This will be useful during debugging to both catch when cache maintenance
is missed and when there is unnecessary cache maintenance.

Change-Id: I1432454a7ab735a63970b977656e9c4c9b5f5be7
Signed-off-by: Liam Mark <lmark@codeaurora.org>