tools/testing/cxl: Set Shutdown State support

Add support to emulate the CXL Set Shutdown State operation.

Signed-off-by: Davidlohr Bueso <dave@stgolabs.net>
Reviewed-by: Dave Jiang <dave.jiang@intel.com>
Reviewed-by: Li Ming <ming.li@zohomail.com>
Reviewed-by: Ira Weiny <ira.weiny@intel.com>
Reviewed-by: Jonathan Cameron <Jonathan.Cameron@huawei.com>
Link: https://patch.msgid.link/20250220220235.276831-5-dave@stgolabs.net


Signed-off-by: Dave Jiang <dave.jiang@intel.com>