platform: include clk.h in platform.h for imx8 target.

The CLK_CPU macro is undefined for imx8 platform therefore
shall be added.

Signed-off-by: Marcin Rajwa <marcin.rajwa@linux.intel.com>

src/platform/imx8/include/platform/platform.h

@@ -10,6 +10,7 @@
 
 #include <sof/platform.h>
 #include <platform/interrupt.h>
+#include <platform/clk.h>
 
 struct sof;