zephyr: imx8ulp: use zephyr utilities when enabled

Use the Zephyr sys/util.h when Zephyr RTOS is used.

While here, remove sof/lib/cpu.h which is not used.

Signed-off-by: Zhang Peng <peng.zhang_8@nxp.com>

src/platform/imx8ulp/lib/clk.c

@@ -6,11 +6,14 @@
 
 #include <sof/common.h>
 #include <rtos/clk.h>
-#include <sof/lib/cpu.h>
 #include <sof/lib/memory.h>
 #include <sof/lib/notifier.h>
 #include <rtos/sof.h>
 
+#ifdef __ZEPHYR__
+#include <zephyr/sys/util.h>
+#endif
+
 const struct freq_table platform_cpu_freq[] = {
 	{ 528000000, 528000 },
 };