imx8mm_beacon: Switch to binman for generating image

To eliminate a warning when using custom imx tools for generating
a binary, use binman to generate flash.bin.

Signed-off-by: Adam Ford <aford173@gmail.com>
Signed-off-by: Marcel Ziswiler <marcel.ziswiler@toradex.com>
Reviewed-by: Simon Glass <sjg@chromium.org>
diff --git a/board/beacon/imx8mm/README b/board/beacon/imx8mm/README
index dce176f..03d9412 100644
--- a/board/beacon/imx8mm/README
+++ b/board/beacon/imx8mm/README
@@ -12,8 +12,8 @@
 Note: $(srctree) is U-Boot source directory
 
 $ git clone https://source.codeaurora.org/external/imx/imx-atf
-$ git checkout imx_4.19.35_1.0.0
-$ make PLAT=imx8mm bl31 ARCH=arm CROSS_COMPILE=aarch64-linux-gnu-
+$ git checkout imx_5.4.70_2.3.0
+$ make PLAT=imx8mm bl31 CROSS_COMPILE=aarch64-linux-gnu-
 $ cp build/imx8mm/release/bl31.bin $(srctree)
 
 Get the DDR firmware
@@ -26,7 +26,7 @@
 Build U-Boot
 ============
 $ make imx8mm_beacon_defconfig
-$ make flash.bin CROSS_COMPILE=aarch64-linux-gnu- ATF_LOAD_ADDR=0x920000
+$ make flash.bin CROSS_COMPILE=aarch64-linux-gnu-
 
 Burn U-Boot to microSD Card
 ===========================