Let the platform's Kconfig to select the clock instead of having a reverse
dependency from the driver to the platform options.

Add the COMPILE_TEST option for the compilation test coverage. Due to the
non portable 'delay' code, this driver is only compilable on ARM.
Signed-off-by: NDaniel Lezcano <daniel.lezcano@linaro.org>
Tested-by: NKrzysztof Kozlowski <k.kozlowski@samsung.com>
Reviewed-by: NKrzysztof Kozlowski <k.kozlowski@samsung.com>
Reviewed-by: NChanwoo Choi <cw00.choi@samsung.com>