cpuidle: mvebu: clean up multiple platform drivers

There's no need to use multiple platform drivers, especially when we
want to do something different in the probe, but we still use a common
probe function.

We can use the platform ID system to only register one platform driver,
but have it match several devices, and give us the CPU idle driver via
the ID's driver_data.

Signed-off-by: Russell King <rmk+kernel@arm.linux.org.uk>
Signed-off-by: Daniel Lezcano <daniel.lezcano@linaro.org>