PCI: Protect Link Control 2 Register with RMW locking

PCI: Protect Link Control 2 Register with RMW locking

The PCIe Bandwidth Controller performs RMW accesses the Link Control 2
Register which can occur concurrently to other sources of Link Control 2
Register writes. Therefore, add Link Control 2 Register among the PCI
Express Capability Registers that need RMW locking.

Link: https://lore.kernel.org/r/20241018144755.7875-3-ilpo.jarvinen@linux.intel.com
Signed-off-by: Ilpo Järvinen <ilpo.jarvinen@linux.intel.com>
Signed-off-by: Bjorn Helgaas <bhelgaas@google.com>
Reviewed-by: Lukas Wunner <lukas@wunner.de>
Reviewed-by: Jonathan Cameron <Jonathan.Cameron@huawei.com>