drivers: thermal: Remove ARCH_HAS_BANDGAP dependency for samsung

As samsung thermal support is enabled only for ARCH_EXYNOS, there is no
need to select ARCH_HAS_BANDGAP from the arch-specific code. Removing this
dependency will also allow the driver to be enabled on 64-bit SoCs.

Reviewed-by: Bartlomiej Zolnierkiewicz <b.zolnierkie@samsung.com>
Reviewed-by: Lukasz Majewski <l.majewski@samsung.com>
Acked-by: Lukasz Majewski <l.majewski@samsung.com>
Signed-off-by: Abhilash Kesavan <a.kesavan@samsung.com>
Signed-off-by: Eduardo Valentin <edubezval@gmail.com>