drm/vkms: Allow to configure connector status via configfs

drm/vkms: Allow to configure connector status via configfs

When a connector is created, add a `status` file to allow to update the
connector status to:

 - 1 connector_status_connected
 - 2 connector_status_disconnected
 - 3 connector_status_unknown

If the device is enabled, updating the status hot-plug or unplugs the
connector.

Tested-by: Mark Yacoub <markyacoub@google.com>
Reviewed-by: Louis Chauvet <louis.chauvet@bootlin.com>
Reviewed-by: Harry Wentland <harry.wentland@amd.com>
Reviewed-by: Luca Ceresoli <luca.ceresoli@bootlin.com>
Signed-off-by: José Expósito <jose.exposito89@gmail.com>
Link: https://lore.kernel.org/r/20251016175618.10051-17-jose.exposito89@gmail.com
Signed-off-by: Luca Ceresoli <luca.ceresoli@bootlin.com>