thermal: imx: depend on imx SoC arch

Not much use unless the SoC is selected so depend on the ARCH_MXC
and COMPILE_TEST like all the other thermal drivers.

v2: drop extraneous OF

Signed-off-by: Peter Robinson <pbrobinson@gmail.com>
Acked-by: Shawn Guo <shawn.guo@linaro.org>
Signed-off-by: Zhang Rui <rui.zhang@intel.com>