drm: improve the documentation of connector hpd ops

drm: improve the documentation of connector hpd ops

While making the changes in [1], it was noted that the documentation
of the enable_hpd() and disable_hpd() does not make it clear that
these ops should not try to do hpd state maintenance and should only
enable/disable hpd related hardware for the connector.

The state management of these calls to make sure these calls are
balanced is handled by the DRM core and we should keep it that way
to minimize the overhead in the drivers which implement these ops.

[1]: https://patchwork.freedesktop.org/patch/558387/

Signed-off-by: Abhinav Kumar <quic_abhinavk@quicinc.com>
Suggested-by: Laurent Pinchart <laurent.pinchart@ideasonboard.com>
Reviewed-by: Laurent Pinchart <laurent.pinchart@ideasonboard.com>
Signed-off-by: Dmitry Baryshkov <dmitry.baryshkov@linaro.org>
Link: https://patchwork.freedesktop.org/patch/msgid/20230920201358.27597-1-quic_abhinavk@quicinc.com