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/freescale/imx8qxp_mek/imx8qxp_mek.c b/board/freescale/imx8qxp_mek/imx8qxp_mek.c
index 21cfa14..516cefd 100644
--- a/board/freescale/imx8qxp_mek/imx8qxp_mek.c
+++ b/board/freescale/imx8qxp_mek/imx8qxp_mek.c
@@ -16,7 +16,7 @@
 #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/snvs_security_sc.h>
 #include <asm/arch/iomux.h>