Bluetooth: GATT: Auto init if bt_gatt_service_register is called

This ensures the core services are always registered first and the
gatt_sc work is initialized.

Fixes #9785

Signed-off-by: Luiz Augusto von Dentz <luiz.von.dentz@intel.com>
Signed-off-by: Anas Nashif <anas.nashif@intel.com>