For ppc64, PAPR requires the nvdimm device to have UUID property
set in the device tree. Add an option to get it from the user.

Signed-off-by: Shivaprasad G Bhat <sbhat@linux.ibm.com>
Reviewed-by: David Gibson <david@gibson.dropbear.id.au>
Reviewed-by: Igor Mammedov <imammedo@redhat.com>
Message-Id: <158131056931.2897.14057087440721445976.stgit@lep8c.aus.stglabs.ibm.com>
Signed-off-by: David Gibson <david@gibson.dropbear.id.au>