[POWERPC] Fix performance monitor on machines with logical PVR

Some IBM machines supply a "logical" PVR (processor version register)
value in the device tree in the cpu nodes rather than the real PVR.
This is used for instance to indicate that the processors in a POWER6
partition have been configured by the hypervisor to run in POWER5+
mode rather than POWER6 mode.  To cope with this, we call identify_cpu
a second time with the logical PVR value (the first call is with the
real PVR value in the very early setup code).

However, POWER5+ machines can also supply a logical PVR value, and use
the same value (the value that indicates a v2.04 architecture
compliant processor).  This causes problems for code that uses the
performance monitor (such as oprofile), because the PMU registers are
different in POWER6 (even in POWER5+ mode) from the real POWER5+.

This change works around this problem by taking out the PMU
information from the cputable entries for the logical PVR values, and
changing identify_cpu so that the second call to it won't overwrite
the PMU information that was established by the first call (the one
with the real PVR), but does update the other fields.  Specifically,
if the cputable entry for the logical PVR value has num_pmcs == 0,
none of the PMU-related fields get used.

So that we can create a mixed cputable entry, we now make cur_cpu_spec
point to a single static struct cpu_spec, and copy stuff from
cpu_specs[i] into it.  This has the side-effect that we can now make
cpu_specs[] be initdata.

Ultimately it would be good to move the PMU-related fields out to a
separate structure, pointed to by the cputable entries, and change
identify_cpu so that it saves the PMU info pointer, copies the whole
structure, and restores the PMU info pointer, rather than identify_cpu
having to list all the fields that are *not* PMU-related.

Signed-off-by: Paul Mackerras <paulus@samba.org>
Acked-by: Benjamin Herrenschmidt <benh@kernel.crashing.org>