sparc64: show time stamps from zero

On most platforms, time is shown from the beginning of boot.  This patch is
adding offset to sched_clock() for SPARC, to also show time from 0.

This means we will have one more load, but we saved one in an ealier patch.

Signed-off-by: Pavel Tatashin <pasha.tatashin@oracle.com>
Reviewed-by: Bob Picco <bob.picco@oracle.com>
Reviewed-by: Steven Sistare <steven.sistare@oracle.com>
Signed-off-by: David S. Miller <davem@davemloft.net>