dts: Documentation: Add documentation for Exynos7 SoC thermal bindings

	       "samsung,exynos5420-tmu-ext-triminfo" for TMU channels 2, 3 and 4

			Exynos5420 (Must pass triminfo base and triminfo clock)

	       "samsung,exynos5440-tmu"

	       "samsung,exynos7-tmu"

- interrupt-parent : The phandle for the interrupt controller

- reg : Address range of the thermal registers. For soc's which has multiple

	instances of TMU and some registers are shared across all TMU's like

- clocks : The main clocks for TMU device

	-- 1. operational clock for TMU channel

	-- 2. optional clock to access the shared registers of TMU channel

	-- 3. optional special clock for functional operation

- clock-names : Thermal system clock name

	-- "tmu_apbif" operational clock for current TMU channel

	-- "tmu_triminfo_apbif" clock to access the shared triminfo register

		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.