cpuidle: kirkwood: Remove ARCH_KIRKWOOD dependency

mach-kirkwood has been removed, now that kirkwood lives in mach-mvebu.
Use MACH_KIRKWOOD, which is set when kirkwood is built as part of
mach-mvebu.

Signed-off-by: Andrew Lunn <andrew@lunn.ch>
Cc: Daniel Lezcano <daniel.lezcano@linaro.org>
Cc: Rafael J. Wysocki <rjw@rjwysocki.net>
Cc: linux-pm@vger.kernel.org
Acked-by: Daniel Lezcano <daniel.lezcano@linaro.org>
Acked-by: Rafael J. Wysocki <rjw@rjwysocki.net>
Link: https://lkml.kernel.org/r/1409417172-6846-2-git-send-email-andrew@lunn.ch


Signed-off-by: Jason Cooper <jason@lakedaemon.net>