cpu: Replace qemu_for_each_cpu()

cpu: Replace qemu_for_each_cpu()

It was introduced to loop over CPUs from target-independent code, but
since commit 182735efaf956ccab50b6d74a4fed163e0f35660 target-independent
CPUState is used.

A loop can be considered more efficient than function calls in a loop,
and CPU_FOREACH() hides implementation details just as well, so use that
instead.

Suggested-by: Markus Armbruster <[email protected]>
Acked-by: Michael S. Tsirkin <[email protected]>
Signed-off-by: Andreas Färber <[email protected]>