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/Kconfig b/board/beacon/imx8mm/Kconfig
index 58799c1..63f064e 100644
--- a/board/beacon/imx8mm/Kconfig
+++ b/board/beacon/imx8mm/Kconfig
@@ -10,7 +10,7 @@
 	default "imx8mm_beacon"
 
 config IMX_CONFIG
-	default "arch/arm/mach-imx/imx8m/imximage-8mm-lpddr4.cfg"
+	default "board/beacon/imx8mm/imximage-8mm-lpddr4.cfg"
 
 source "board/freescale/common/Kconfig"