thermal: uniphier: add UniPhier thermal driver

Add a thermal driver for on-chip PVT (Process, Voltage and Temperature)
monitoring unit implemented on UniPhier SoCs. This driver supports
temperature monitoring and alert function.

Signed-off-by: Kunihiko Hayashi <hayashi.kunihiko@socionext.com>
Signed-off-by: Zhang Rui <rui.zhang@intel.com>