libnvdimm: Drop unused device power management support

LIBNVDIMM device objects register sysfs power attributes despite nothing
requiring that support. Clean up sysfs remove the power/ attribute
group. This requires a device_create() and a device_register() usage to
be converted to the device_initialize() + device_add() pattern.

Reviewed-by: Jonathan Cameron <Jonathan.Cameron@huawei.com>
Link: https://lore.kernel.org/r/162379910795.2993820.10130417680551632288.stgit@dwillia2-desk3.amr.corp.intel.com


Signed-off-by: Dan Williams <dan.j.williams@intel.com>