clk: imx: Fix the build break when clk-imx8ulp build as module

Export the necessary symbols to fix the build break when clk-imx8ulp
build as module

Fixes: c43a801a

 ("clk: imx: Add clock driver for imx8ulp")
Signed-off-by: Jacky Bai <ping.bai@nxp.com>
Reviewed-by: Abel Vesa <abel.vesa@nxp.com>
Link: https://lore.kernel.org/r/20210917061629.3798360-1-ping.bai@nxp.com
Signed-off-by: Abel Vesa <abel.vesa@nxp.com>