soc: imx: drop COMPILE_TEST for IMX_SCU_SOC

With COMPILE_TEST, there will be build error, because IMX_SCU
might be set to n, so drop COMPILE_TEST.

Suggested-by: Shawn Guo <shawnguo@kernel.org>
Signed-off-by: Peng Fan <peng.fan@nxp.com>
Signed-off-by: Shawn Guo <shawnguo@kernel.org>