MIPS: Loongson: Reduce possible loop times and add log in do_thermal_timer()

Once the temperature of any CPUs is too high, it can power off immediately,
no need to check the rest of CPUs, and it is better to print a log before
power off, this is useful when analysis the abnormal issues.

Signed-off-by: Tiezhu Yang <yangtiezhu@loongson.cn>
Signed-off-by: Zhi Li <lizhi01@loongson.cn>
Signed-off-by: Thomas Bogendoerfer <tsbogend@alpha.franken.de>