thermal: core: using power_efficient_wq for thermal worker

For SMP systems, thermal worker should use power_efficient_wq in power
saving mode, that will make scheduler more flexible on selecting an active
core for running work handler to avoid keeping work handler always
running on a single core, that will save some power.

Even if 'power_efficient_wq' relevant configs are disabled
'system_freezable_power_efficient_wq' is identical to system_freezable_wq,
behavior is unchanged.

Signed-off-by: Jeson Gao <jeson.gao@unisoc.com>
Signed-off-by: Chunyan Zhang <chunyan.zhang@unisoc.com>
Signed-off-by: Zhang Rui <rui.zhang@intel.com>