drivers: soc: samsung: Enable COMPILE_TEST

Get some build coverage of Exynos PMU driver. It depends on
asm/cputype.h so its compilation is limited to ARM architectures.

Signed-off-by: Krzysztof Kozlowski <k.kozlowski@samsung.com>
Reviewed-by: Javier Martinez Canillas <javier@osg.samsung.com>