msm: rq_stats: Disable hotplug and stats by default

Userspace closed source mpdecision binary is nessecary for PowerHAL to work.
As it depends on rq_stats, let's at least disable hotplugging and stats
collection by default. /sys/devices/system/cpu/cpu0/rq-stats/hotplug_disable
is now writable, so hotplug can be reenabled.

Also, add some bits related to current cpu policy.
Revert "defconfig: Disable MSM Run Queue stats"

This reverts commit 2edd2bb9cd59bf8efc0f95c781b9f7096ef75c56.
msm: hotplug: On- and offline cpus only when enabled

I mean really, really enabled...
sched: Calculate max_possible_freq based on current policy->max
cpufreq: ondemand: Calculate load_at_max_freq based on current policy->max