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/board/advantech/imx8qm_dmsse20_a1/spl.c b/board/advantech/imx8qm_dmsse20_a1/spl.c
index 49067bb..7f2e972 100644
--- a/board/advantech/imx8qm_dmsse20_a1/spl.c
+++ b/board/advantech/imx8qm_dmsse20_a1/spl.c
@@ -11,7 +11,7 @@
 #include <asm/io.h>
 #include <asm/gpio.h>
 #include <asm/arch/clock.h>
-#include <asm/arch/sci/sci.h>
+#include <firmware/imx/sci/sci.h>
 #include <asm/arch/imx8-pins.h>
 #include <asm/arch/iomux.h>
 #include <fsl_esdhc_imx.h>