msm: camera: isp: Fix CTS issue for RDI stream

- For RDI stream, reg_update is done during reg_update_ack
in tasklet context. So, frame drop cannot be added since
epoch is not received for pure RDI stream. To take of this,
Add PIX stream check to avoid drop frame logic.
- Reset reg_update_requested flag during stop_axi_stream
and request_axi_stream to make sure it is not carry-forwarded
for next stream.

Change-Id: I44b75d9ad27cdca968aef08156833389b666199a
Signed-off-by: Sreesudhan Ramakrish Ramkumar <srramku@codeaurora.org>