imx8qxp: mek: update README

Update README after we switch to use SPL

Signed-off-by: Peng Fan <peng.fan@nxp.com>
diff --git a/board/freescale/imx8qxp_mek/README b/board/freescale/imx8qxp_mek/README
index e91e193..f32290e 100644
--- a/board/freescale/imx8qxp_mek/README
+++ b/board/freescale/imx8qxp_mek/README
@@ -39,16 +39,18 @@
 
 Build U-Boot
 ============
-
+$ export ATF_LOAD_ADDR=0x80000000
+$ export BL33_LOAD_ADDR=0x80020000
 $ make imx8qxp_mek_defconfig
-$ make
+$ make flash.bin
+$ dd if=u-boot.itb of=flash.bin bs=512 seek=528
 
 Flash the binary into the SD card
 =================================
 
 Burn the flash.bin binary to SD card offset 32KB:
 
-$ sudo dd if=u-boot-dtb.imx of=/dev/sd[x] bs=1024 seek=32
+$ sudo dd if=flash.bin of=/dev/sd[x] bs=1024 seek=32
 
 Boot
 ====