drm/connector: Give connector sysfs devices there own device_type

Give connector sysfs devices there own device_type, this allows us to
check if a device passed to functions dealing with generic devices is
a drm_connector or not.

A check like this is necessary in the drm_connector_acpi_bus_match()
function added in the next patch in this series.

Tested-by: Heikki Krogerus <heikki.krogerus@linux.intel.com>
Signed-off-by: Hans de Goede <hdegoede@redhat.com>
Reviewed-by: Lyude Paul <lyude@redhat.com>
Link: https://lore.kernel.org/r/20210817215201.795062-2-hdegoede@redhat.com