dmaengine: ioatdma: Ignore IOAT devices under hotplug-capable PCI host bridge

The dmaengine core assumes that async DMA devices will only be removed
when they not used anymore, or it assumes dma_async_device_unregister()
will only be called by dma driver exit routines. But this assumption is
not true for the IOAT driver, which calls dma_async_device_unregister()
from ioat_remove(). So current IOAT driver doesn't support device
hot-removal because it may cause system crash to hot-remove an inuse
IOAT device.

To support CPU socket hot-removal, all PCI devices, including IOAT
devices embedded in the socket, will be hot-removed. The idea solution
is to enhance the dmaengine core and IOAT driver to support hot-removal,
but that's too hard.

This patch implements a hack to disable IOAT devices under hotplug-capable
CPU socket so it won't break socket hot-removal.

Signed-off-by: Jiang Liu <jiang.liu@linux.intel.com>
Signed-off-by: Vinod Koul <vinod.koul@intel.com>