intelli-thermal: use its own dedicated workqueue

this should reduce the load on the shared global workqueue for other
processes and also give its own unique variable name for cpu limit

(from me) I've updated the M7 source code, idea is taken here -
https://github.com/faux123/Nexus_5/commit/2ed9831e0ebb3df3380fdf32da0bfe76a392d738