cxl/pmem: add provider name to cxl pmem dimm attribute group

Add provider name in order to associate cxl test dimm from cxl_test to the
cxl pmem device when going through sysfs for security testing.

Reviewed-by: Jonathan Cameron <Jonathan.Cameron@huawei.com>
Signed-off-by: Dave Jiang <dave.jiang@intel.com>
Link: https://lore.kernel.org/r/166983618174.2734609.15600031015423828810.stgit@djiang5-desk3.ch.intel.com
Signed-off-by: Dan Williams <dan.j.williams@intel.com>