drm/i915: Don't change the status of forced connectors during hotplug detect

DRM display connectors forced to a connected/disconnected state via the
drm_connector::force member shouldn't change their status. Atm, this can
still happen in the connector's detect function when called to handle a
hotplug event. This in turn may lead to the GETCONNECTOR ioctl to report
the incorrect state if it's called to return the connector properties
without doing an actual detection (by calling the ioctl with a non-zero
drm_mode_get_connector::count_modes).

Fix the above by updating the connector state during hotplug detect only
if the connector state is not forced.

Testcase: igt@kms_force_connector_basic@force-connector-state
Signed-off-by: Imre Deak <imre.deak@intel.com>
Reviewed-by: Jouni Högander <jouni.hogander@intel.com>
Link: https://patchwork.freedesktop.org/patch/msgid/20230809104307.1218058-2-imre.deak@intel.com