sparc64: add MDESC node name property to VIO device metadata

Add the MDESC node name of MDESC client to VIO device metadata. It is
later used to uniquely identify a node in the MDESC. VIO & MDESC APIs
are updated to handle this node name.

Signed-off-by: Jagannathan Raman <jag.raman@oracle.com>
Reviewed-by: Liam Merwick <liam.merwick@oracle.com>
Reviewed-by: Shannon Nelson <shannon.nelson@oracle.com>
Signed-off-by: David S. Miller <davem@davemloft.net>