thermal: exynos: List vtmu-supply as optional property in DT binding

The Exynos Thermal Management Unit binding says that the vtmu-supply
is optional but is listed in the required properties section. Add an
optional properties section and move the regulator property there.
Acked-by: NRob Herring <robh@kernel.org>
Reviewed-by: NKrzysztof Kozlowski <k.kozlowski@samsung.com>
Reviewed-by: NAndi Shyti <andi.shyti@samsung.com>
Signed-off-by: NJavier Martinez Canillas <javier@osg.samsung.com>
Signed-off-by: NEduardo Valentin <edubezval@gmail.com>

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

@@ -41,9 +41,6 @@
 		for current TMU channel
 	-- "tmu_sclk" clock for functional operation of the current TMU
 		channel
-- 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
@@ -65,6 +62,12 @@ Following properties are mandatory (depending on SoC):
 - samsung,tmu_default_temp_offset: Default temperature offset
 - samsung,tmu_cal_type: Callibration type
 
+** Optional properties:
+
+- 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.
+
 Example 1):
 
 	tmu@100C0000 {