powerpc/smp: Cache CPU to chip lookup

On systems with large CPUs per node, even with the filtered matching of
related CPUs, there can be large number of calls to cpu_to_chip_id for
the same CPU. For example with 4096 vCPU, 1 node QEMU configuration,
with 4 threads per core, system could be see upto 1024 calls to
cpu_to_chip_id() for the same CPU. On a given system, cpu_to_chip_id()
for a given CPU would always return the same. Hence cache the result in
a lookup table for use in subsequent calls.

Since all CPUs sharing the same core will belong to the same chip, the
lookup_table has an entry for one CPU per core.  chip_id_lookup_table is
not being freed and would be used on subsequent CPU online post CPU
offline.

Reported-by: Daniel Henrique Barboza <[email protected]>
Suggested-by: Michael Ellerman <[email protected]>
Signed-off-by: Srikar Dronamraju <[email protected]>
Tested-by: Daniel Henrique Barboza <[email protected]>
Signed-off-by: Michael Ellerman <[email protected]>
Link: https://lore.kernel.org/r/[email protected]

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