imx: move imx8 sci header file to include/firmware/imx

Move imx8 sci header file to include/firmware/imx, then we could
use build macro to reuse some i.MX8 drivers for i.MX9, such as
drivers/cpu/imx8_cpu.c.

Signed-off-by: Peng Fan <peng.fan@nxp.com>
Signed-off-by: Stefano Babic <sbabic@denx.de>
diff --git a/arch/arm/mach-imx/imx8/iomux.c b/arch/arm/mach-imx/imx8/iomux.c
index 9c3cfbf..e4f7651 100644
--- a/arch/arm/mach-imx/imx8/iomux.c
+++ b/arch/arm/mach-imx/imx8/iomux.c
@@ -8,7 +8,7 @@
 #include <asm/global_data.h>
 #include <asm/io.h>
 #include <asm/arch/iomux.h>
-#include <asm/arch/sci/sci.h>
+#include <firmware/imx/sci/sci.h>
 
 DECLARE_GLOBAL_DATA_PTR;