add backup_serial_console option

Signed-off-by: Robert Nelson <robertcnelson@gmail.com>

lib/distro_defaults.cmd

@@ -38,6 +38,12 @@ for i in 1 2 3 4 5 6 7 ; do
 			echo Using: [rootfstype=ext4] ...;
 		fi;
 
+		if test -n ${console}; then
+			if test -n ${backup_serial_console}; then
+				setenv console ${backup_serial_console}
+			fi ;
+		fi ;
+
 		if test -n ${uname_r}; then
 			setenv bootdir /boot;
 			setenv bootfile vmlinuz-${uname_r};

mk_mmc.sh

@@ -1154,6 +1154,10 @@ populate_boot () {
 			echo "#dtb=" >>  ${wfile}
 		fi
 
+		if [ ! "x${SERIAL_CONSOLE}" = "x" ] ; then
+			echo "backup_serial_console=${SERIAL_CONSOLE}" >> ${wfile}
+		fi
+
 		mmcargs="mmcargs=run message; setenv bootargs console"
 
 		if [ "x${di_serial_mode}" = "xenable" ] ; then