powerpc/cputable: Fix oprofile_cpu_type on power8

Maynard informed me that neither the oprofile kernel module nor oprofile
userspace has been updated to support that "legacy" oprofile module
interface for power8, which is indicated by "ppc64/power8." This results
in no samples. The solution is to default to the "timer" type, instead.
The raw entry also should be updated, as "ppc64/ibm-compat-v1" indicates
to oprofile userspace to use "compatibility events" which are obsolete
in ISA 2.07.

Signed-off-by: Nishanth Aravamudan <nacc@us.ibm.com>
Signed-off-by: Benjamin Herrenschmidt <benh@kernel.crashing.org>