libnvdimm: Convert to DEVICE_ATTR_ADMIN_RO()

Move libnvdimm sysfs attributes that currently use an open coded
DEVICE_ATTR() to hide sensitive root-only information (physical memory
layout) to the new DEVICE_ATTR_ADMIN_RO() helper.

Cc: Vishal Verma <vishal.l.verma@intel.com>
Cc: Dave Jiang <dave.jiang@intel.com>
Cc: Ira Weiny <ira.weiny@intel.com>
Signed-off-by: Dan Williams <dan.j.williams@intel.com>
Signed-off-by: Vishal Verma <vishal.l.verma@intel.com>