thermal: exynos: allow compile test

Adding COMPILE_TEST flag to exynos driver to facilitate
maintenance.

Cc: Lukasz Majewski <l.majewski@samsung.com>
Cc: Zhang Rui <rui.zhang@intel.com>
Cc: linux-pm@vger.kernel.org
Cc: linux-samsung-soc@vger.kernel.org
Cc: linux-kernel@vger.kernel.org
Signed-off-by: Eduardo Valentin <edubezval@gmail.com>