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/configs/imx8mm_beacon_defconfig b/configs/imx8mm_beacon_defconfig
index de00543..9aea5bf 100644
--- a/configs/imx8mm_beacon_defconfig
+++ b/configs/imx8mm_beacon_defconfig
@@ -21,7 +21,7 @@
 CONFIG_FIT=y
 CONFIG_FIT_EXTERNAL_OFFSET=0x3000
 CONFIG_SPL_LOAD_FIT=y
-CONFIG_SPL_FIT_GENERATOR="arch/arm/mach-imx/mkimage_fit_atf.sh"
+# CONFIG_USE_SPL_FIT_GENERATOR is not set
 CONFIG_OF_SYSTEM_SETUP=y
 CONFIG_DEFAULT_FDT_FILE="imx8mm-beacon-kit.dtb"
 CONFIG_SPL_BOARD_INIT=y