powerpc: Deindentify identify_cpu()

The for-loop body of identify_cpu() has gotten a little big, so move the
loop body logic into a separate function. No other changes.

Signed-off-by: Michael Ellerman <michael@ellerman.id.au>
Acked-by: Dave Kleikamp <shaggy@linux.vnet.ibm.com>
Signed-off-by: Benjamin Herrenschmidt <benh@kernel.crashing.org>