sparc: update copyright in piggyback.c

Update copyright info in piggyback.c to include
info from piggyback_64.c.
Include my own copyright too.

Signed-off-by: Sam Ravnborg <sam@ravnborg.org>
Cc: Josip Rodin <joy@entuzijast.net>
Cc: Jakub Jelinek <jakub@redhat.com>
Signed-off-by: David S. Miller <davem@davemloft.net>