thermal: exynos: Document number of supported trip-points

Document the number of configurable temperature thresholds (for
trip-points in interrupt-driven mode).

Acked-by: Rob Herring <robh@kernel.org>
Reviewed-by: Chanwoo Choi <cw00.choi@samsung.com>
Signed-off-by: Krzysztof Kozlowski <k.kozlowski@samsung.com>
Signed-off-by: Eduardo Valentin <edubezval@gmail.com>

Documentation/devicetree/bindings/thermal/exynos-thermal.txt

@@ -44,6 +44,14 @@
 - vtmu-supply: This entry is optional and provides the regulator node supplying
 		voltage to TMU. If needed this entry can be placed inside
 		board/platform specific dts file.
+
+The Exynos TMU supports generating interrupts when reaching given
+temperature thresholds. Number of supported thermal trip points depends
+on the SoC (only first trip points defined in DT will be configured):
+ - most of SoC: 4
+ - samsung,exynos5433-tmu: 8
+ - samsung,exynos7-tmu: 8
+
 Following properties are mandatory (depending on SoC):
 - samsung,tmu_gain: Gain value for internal TMU operation.
 - samsung,tmu_reference_voltage: Value of TMU IP block's reference voltage