FROMGIT: dt-bindings: thermal: sprd: Add the Spreadtrum thermal documentation

Add the Spreadtrum thermal documentation.

bug: 151273001
Signed-off-by: Baolin Wang <baolin.wang@unisoc.com>
Signed-off-by: Baolin Wang <baolin.wang7@gmail.com>
Reviewed-by: Rob Herring <robh@kernel.org>
Signed-off-by: Daniel Lezcano <daniel.lezcano@linaro.org>
Link: https://lore.kernel.org/r/444e45ce0a9b390b2502dfcefd1ddb36948fa8e1.1582013101.git.baolin.wang7@gmail.com
(cherry picked from commit 526736a5fc84ebbe2bfd6796ff67d1c68c50a624
https://git.kernel.org/pub/scm/linux/kernel/git/thermal/linux.git thermal/linux-next)