package/ffmpeg: mmal is not available on aarch64

Fixes:
http://autobuild.buildroot.net/results/aa5/aa589b38e1591a0ec4d400891bf86f5138cf4542/

For details see:
https://lists.buildroot.org/pipermail/buildroot/2023-July/669839.html
https://github.com/raspberrypi/userland/issues/688

Reported-by: Guillermo G <ggalan3@gmail.com>
Signed-off-by: Bernd Kuhls <bernd@kuhls.net>
Signed-off-by: Thomas Petazzoni <thomas.petazzoni@bootlin.com>

package/ffmpeg/ffmpeg.mk

@@ -282,9 +282,14 @@ FFMPEG_CONF_OPTS += --disable-vdpau
 endif
 
 ifeq ($(BR2_PACKAGE_RPI_USERLAND),y)
-FFMPEG_CONF_OPTS += --enable-mmal --enable-omx --enable-omx-rpi \
+FFMPEG_CONF_OPTS += --enable-omx --enable-omx-rpi \
 	--extra-cflags=-I$(STAGING_DIR)/usr/include/IL
 FFMPEG_DEPENDENCIES += rpi-userland
+ifeq ($(BR2_arm),y)
+FFMPEG_CONF_OPTS += --enable-mmal
+else
+FFMPEG_CONF_OPTS += --disable-mmal
+endif
 else
 FFMPEG_CONF_OPTS += --disable-mmal --disable-omx --disable-omx-rpi
 endif