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/drivers/power/domain/imx8-power-domain-legacy.c b/drivers/power/domain/imx8-power-domain-legacy.c
index bf45891..37b0f95 100644
--- a/drivers/power/domain/imx8-power-domain-legacy.c
+++ b/drivers/power/domain/imx8-power-domain-legacy.c
@@ -14,7 +14,7 @@
 #include <dm/device-internal.h>
 #include <dm/device.h>
 #include <dm/uclass-internal.h>
-#include <asm/arch/sci/sci.h>
+#include <firmware/imx/sci/sci.h>
 
 DECLARE_GLOBAL_DATA_PTR;