ARM: exynos: no need to select ARCH_HAS_BANDGAP any longer

This is not needed since commit fcbb1e02 ("drivers: thermal:
Remove ARCH_HAS_BANDGAP dependency for samsung") from 2014.

Signed-off-by: Bartlomiej Zolnierkiewicz <b.zolnierkie@samsung.com>
Signed-off-by: Krzysztof Kozlowski <krzk@kernel.org>