platform: mips: cpu_hwmon: Disable driver on unsupported hardware

cpu_hwmon is unsupported on CPUs without loongson_chiptemp
register and csr.

Cc: stable@vger.kernel.org
Signed-off-by: Jiaxun Yang <jiaxun.yang@flygoat.com>
Signed-off-by: Thomas Bogendoerfer <tsbogend@alpha.franken.de>