msm: thermal: Always initialize frequency mitigation thread

Add support for kernel thermal monitor (KTM) to initialize the
frequency mitigation thread irrespective of the frequency
mitigation devicetree property. This is to facilitate the
userspace cpu frequency mitigation using thermal IOCTL
interface.

Change-Id: Ifea70772d02f4875544aaa6a1a08ad9b5612131c
Signed-off-by: Ram Chandrasekar <rkumbako@codeaurora.org>