cpuquiet: Add Sysfs node for nr_run_thresholds

cpuquiet: Add Sysfs node for nr_run_thresholds

Added sysfs node that exposes the nr_runnable threshold at which cores
are quiesenced/woken up. To write into this node:

echo 1core# 2core# ... n_core# > nr_run_thresholds

Bug 1427140

Change-Id: I7cabd63692cf92f7fe8d1064437b1d73002d4ba5
Signed-off-by: Sai Gurrappadi <sgurrappadi@nvidia.com>
Reviewed-on: http://git-master/r/369017
Reviewed-by: Automatic_Commit_Validation_User
GVS: Gerrit_Virtual_Submit
Reviewed-by: Diwakar Tundlam <dtundlam@nvidia.com>