Camera: Make sure timestamp is increasing

Guard against case where timestamp of stream buffers doesn't increase.

Timestamp source is either monotonic or boottime, both of which are
guaranteed to increase.

There are 2 exceptions where timestamp may go back in time:
- For requests where HAL ZSL is enabled, and
- For reprocessing requests

Test: Camera CTS
Bug: 113340974
Change-Id: I0ae9290696d651168150fa5ed7aa13c140a0294f