thermal: set emul_temp when thermal-disabled prop is enabled

powerhint will re-enable skin-therm-cpu after device reboot, so we need
to set emul_temp to prevent triggering CPU throttling for perf PTS test.

Bug: 159105102
Test: emul_temp can be set to 25 degC when thermal-disabled property is enabled
Change-Id: Ia79188c4770f1372eb272a51cf61f447c32f240d
Signed-off-by: TeYuan Wang <kamewang@google.com>