thermal: sprd: Add Spreadtrum thermal driver support

This patch adds the support for Spreadtrum thermal sensor controller,
which can support maximum 8 sensors.

Signed-off-by: Freeman Liu <freeman.liu@unisoc.com>
Co-developed-with: Baolin Wang <baolin.wang@unisoc.com>
Signed-off-by: Baolin Wang <baolin.wang7@gmail.com>
Signed-off-by: Daniel Lezcano <daniel.lezcano@linaro.org>
Link: https://lore.kernel.org/r/ebeb2839cff4d4027b37e787427c5af0e11880c8.1582013101.git.baolin.wang7@gmail.com