arm: u8500_hotplug: allow configuration of polling delay and add some debugging msgs

Change-Id: I579f97446cdfa83205c339ffe33740a8d2400424
arm: u8500_hotplug: don't online cpu1 immediately, unless load is extremely high

don't online cpu1 immediately, only online after every 5 polls(0.5s by default). unless, of course, the load is very high (95). also export a few more tunables to userspace.

Change-Id: I28342a39f4b93062f56465c03f9b0cadc6a2f1f9
arm: u8500_hotplug: adjust up_timer_threshold to 10

don't need to be such a short timer.

also added some forgotten stuff

Change-Id: I2afb5b53d7d83cfe905017235d9ea695b2b9adbb