cxl/acpi: Move rescan to the workqueue

[ Upstream commit 4029c32f ]

Now that the cxl_mem driver has a need to take the root device lock, the
cxl_bus_rescan() needs to run outside of the root lock context. That
need arises from RCH topologies and the locking that the cxl_mem driver
does to attach a descendant to an upstream port. In the RCH case the
lock needed is the CXL root device lock [1].

Link: http://lore.kernel.org/r/166993045621.1882361.1730100141527044744.stgit@dwillia2-xfh.jf.intel.com

 [1]
Tested-by: Robert Richter <rrichter@amd.com>
Link: http://lore.kernel.org/r/166993042884.1882361.5633723613683058881.stgit@dwillia2-xfh.jf.intel.com


Reviewed-by: Jonathan Cameron <Jonathan.Cameron@huawei.com>
Signed-off-by: Dan Williams <dan.j.williams@intel.com>
Stable-dep-of: 3d6ebf16 ("cxl/port: Fix cxl_bus_rescan() vs bus_rescan_devices()")
Signed-off-by: Sasha Levin <sashal@kernel.org>