Thermal: exynos: Add sysfs node supporting exynos's emulation mode.

This patch supports exynos's emulation mode with newly created sysfs node.
Exynos 4x12 (4212, 4412) and 5 series provide emulation mode for thermal
management unit. Thermal emulation mode supports software debug for TMU's
operation. User can set temperature manually with software code and TMU
will read current temperature from user value not from sensor's value.
This patch includes also documentary placed under Documentation/thermal/.

Signed-off-by: Jonghwa Lee <jonghwa3.lee@samsung.com>
Signed-off-by: Zhang Rui <rui.zhang@intel.com>