drivers: media: cfe: Add more robust ISR handlers

Update the ISR logic to be more robust to sensors in problematic states
where interrupts may start arriving overlapped and/or missing.

1) Test for cur_frame in the FE handler, and if present, dequeue it in
an error state so that it does not get orphaned.

2) Move the sequence counter and timestamp variables to the node
structures.  This allows the ISR to track channels running ahead when
interrupts arrive unordered.

3) Add a test to ensure we don't have a spurios (but harmlesS) call to
the FE handler in some circumstances.

Signed-off-by: Naushir Patuck <naush@raspberrypi.com>