After early boot time stamps project the %tick frequency is detected
incorrectly on spittfire cpus.

We must use cpuid of boot cpu to find corresponding cpu node in OpenBoot,
and extract clock-frequency property from there.
Signed-off-by: NPavel Tatashin <pasha.tatashin@oracle.com>
Signed-off-by: NDavid S. Miller <davem@davemloft.net>