sparc64: check if a client is allowed to register for MDESC notifications

Check if a client is supported, by comparing against a whitelist, to
register for notifications from Machine Description (MDESC)

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>