[PATCH v6] binder: transaction latency tracking for user build

[Frankie Chang]

Change from v6:
  - change CONFIG_BINDER_TRANSACTION_LATENCY_TRACKING type from bool to tristate
  - add comments to @timestamp and @tv under struct binder_transaction
  - make binder_txn_latency threshold configurable
  - enhance lock protection

Change from v5:
  - change config name to the proper one, CONFIG_BINDER_TRANSACTION_LATENCY_TRACKING.
  - change tracepoint name to more descriptive one, trace_binder_txn_latency_(alloc|info|free)
  - enhance some lock protection.

Change from v4:
  - split up into patch series.

Change from v3:
  - use tracepoints for binder_update_info and print_binder_transaction_ext,
    instead of custom registration functions.

Change from v2:
  - create transaction latency module to monitor slow transaction.

Change from v1:
  - first patchset.