powerpc: Split ICSWX ACOP and PID processing

Some processors, like embedded, that already have a PID register that
is managed by the system.  This patch separates the ACOP and PID
processing into separate files so that the ACOP code can be shared.

Signed-off-by: Jimi Xenidis <jimix@pobox.com>
Signed-off-by: Benjamin Herrenschmidt <benh@kernel.crashing.org>