Adds an overflow mechanism for binder calls.

This logic will ensure that we have a limit for the number of items we
track to make sure we do not use too much memory.

We still have an overflow per uid in order to properly attribute the cpu
usage to the uids.

Test: atest BinderCallsStatsTest
Change-Id: Ife9f7249bae35d5c61a6d35ac9d25437d213e959