thermal: exynos: Rename exynos_thermal.c to exynos_tmu.c

This patch renames exynos_thermal.c to exynos_tmu.c. This change is needed as
this file now just contains exynos tmu driver related codes and thermal zone
or cpufreq cooling registration related changes are not there anymore.

Acked-by: Kukjin Kim <kgene.kim@samsung.com>
Acked-by: Jonghwa Lee <jonghwa3.lee@samsung.com>
Acked-by: Eduardo Valentin <eduardo.valentin@ti.com>
Signed-off-by: Amit Daniel Kachhap <amit.daniel@samsung.com>
Signed-off-by: Eduardo Valentin <eduardo.valentin@ti.com>