staging: vc04_services: Move variables for tracking connections

Connections to the vchiq driver are tracked using global variables.
Drop those and introduce them as members of struct vchiq_drv_mgmt.
Hence, struct vchiq_drv_mgmt will be used to track the connections.

Also, store a vchiq_drv_mgmt pointer to struct vchiq_device to
have easy access to struct vchiq_drv_mgmt across vchiq devices.

Reviewed-by: Laurent Pinchart <laurent.pinchart@ideasonboard.com>
Signed-off-by: Umang Jain <umang.jain@ideasonboard.com>
Link: https://lore.kernel.org/r/20240412075743.60712-5-umang.jain@ideasonboard.com
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>