ARM: dts: uniphier: add nodes of thermal monitor and thermal zone for PXs2

Add nodes of thermal monitor and thermal zone for UniPhier PXs2 SoC.
The thermal monitor node is included in sysctrl. Since the efuse might not
have a calibrated value of thermal monitor, this patch gives the default
value for PXs2.

Furthermore, add cpuN labels for reference in cooling-device property.

Signed-off-by: Kunihiko Hayashi <hayashi.kunihiko@socionext.com>
Signed-off-by: Masahiro Yamada <yamada.masahiro@socionext.com>