thermal: cpu_cooling: remove set_freezable() when suspend not implemented

The cpu_cooling driver prevents system suspend due to one hung task per
cpu. This is because it is "set freezable" by accident. That's a bug.

Note: In newer kernels, this issue goes away because of a different
implementation altogether and system suspend will work there.
2 jobs for imx8-current-librem5_20191216_cpuidle_bugfix in 47 minutes and 55 seconds (queued for 22 minutes and 58 seconds)