soc: samsung: exynos-chipid: do not enforce built-in

After converting the Exynos ChipID and ASV driver to a module, allow to
actually choose it to be a module, while being a default built-in.  The
side effect is that driver could be now entirely disabled even for
kernel with ARCH_EXYNOS, but this is not a critical issue because driver
is not necessary for the proper platform boot.

Signed-off-by: Krzysztof Kozlowski <krzysztof.kozlowski@canonical.com>
Reviewed-by: Sylwester Nawrocki <snawrocki@kernel.org>
Tested-by: Sylwester Nawrocki <snawrocki@kernel.org>
Reviewed-by: Alim Akhtar <alim.akhtar@samsung.com>
Tested-by: Alim Akhtar <alim.akhtar@samsung.com>
Link: https://lore.kernel.org/r/20210919093114.35987-4-krzysztof.kozlowski@canonical.com