thermal/drivers/exynos: Simplify regulator (de)initialization

We rewrite the initialization to enable the regulator as part of devm,
which allows us to not handle the struct instance manually.

Reviewed-by: Krzysztof Kozlowski <krzysztof.kozlowski@linaro.org>
Signed-off-by: Mateusz Majewski <m.majewski2@samsung.com>
Signed-off-by: Daniel Lezcano <daniel.lezcano@linaro.org> Link:
https://lore.kernel.org/r/20231201095625.301884-6-m.majewski2@samsung.com