msm: dcvs: prevent thread creations upon cpu hotplug insertions

Numerous threads were seen created and left idle as cpu's were
hotplugged in and out. Avoid creating new threads unnecessarily.

Instead create just one thread when a core is registered and use
it later.

Change-Id: I298c7438fe4850e028bd920808ac180918641c10
Signed-off-by: Abhijeet Dharmapurikar <adharmap@codeaurora.org>