media: iris: Add encoder support for V4L2 event subscription

media: iris: Add encoder support for V4L2 event subscription

Implement support for V4L2 event subscription on the encoder device by
handling the SUBSCRIBE_EVENT and UNSUBSCRIBE_EVENT ioctls with the
necessary hooks.

This enables userspace applications to subscribe to V4L2 events,
allowing asynchronous notification mechanisms.

Tested-by: Vikash Garodia <quic_vgarodia@quicinc.com> # X1E80100
Reviewed-by: Vikash Garodia <quic_vgarodia@quicinc.com>
Tested-by: Neil Armstrong <neil.armstrong@linaro.org> # on SM8550-HDK
Tested-by: Neil Armstrong <neil.armstrong@linaro.org> # on SM8650-HDK
Signed-off-by: Dikshita Agarwal <quic_dikshita@quicinc.com>
Tested-by: Bryan O'Donoghue <bryan.odonoghue@linaro.org> # x1e80100-crd
Signed-off-by: Bryan O'Donoghue <bod@kernel.org>
Signed-off-by: Hans Verkuil <hverkuil+cisco@kernel.org>