thermal: exynos: Use ARCH_HAS_BANDGAP config to know the supported soc's

This patch uses the recently added config sybmol ARCH_HAS_BANDGAP to enable
the TMU driver. This will allow adding support for new soc easily as now it
is the platform responsibility to enable this config symbol for a particular
soc.

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>