imx8ulp: Update flash_kernel target loading address

Since u-boot has updated load address to 0x80400000, need to update
it as well for flash_kernel

Signed-off-by: Ye Li <ye.li@nxp.com>
(cherry picked from commit dc4b1e2b)

iMX8ULP/soc.mak

@@ -133,7 +133,7 @@ flash_sentinel: $(MKIMG) ahabfw.bin
 	./$(MKIMG) -soc ULP -c -sentinel ahabfw.bin -out flash.bin
 
 prepare_kernel_chunks: Image
-	./$(SPLIT_KERNEL) Image 0x80480000 0x700000
+	./$(SPLIT_KERNEL) Image 0x80400000 0x700000
 
 flash_kernel: $(MKIMG) prepare_kernel_chunks imx8ulp-evk.dtb
 	KERNEL_CMD="$(shell cat Image_cmd)"; \