media: iris: Improve last flag handling

Improve the handling of the V4L2_BUF_FLAG_LAST flag in the driver:
- Ensure that the last flag is not sent multiple times.
- Attach the last flag to the first capture buffer returned during
  flush, triggered by a sequence change, addressing cases where the
  firmware does not set the last flag.

Reviewed-by: Vikash Garodia <quic_vgarodia@quicinc.com>
Reviewed-by: Bryan O'Donoghue <bryan.odonoghue@linaro.org>
Tested-by: Neil Armstrong <neil.armstrong@linaro.org> # on SM8550-QRD
Tested-by: Neil Armstrong <neil.armstrong@linaro.org> # on SM8550-HDK
Tested-by: Neil Armstrong <neil.armstrong@linaro.org> # on SM8650-QRD
Tested-by: Neil Armstrong <neil.armstrong@linaro.org> # on SM8650-HDK
Signed-off-by: Dikshita Agarwal <quic_dikshita@quicinc.com>
Tested-by: Vikash Garodia <quic_vgarodia@quicinc.com> # on sa8775p-ride
Signed-off-by: Bryan O'Donoghue <bod@kernel.org>
Signed-off-by: Hans Verkuil <hverkuil@xs4all.nl>