initscripts: Add support for /etc/default/timestamp

Source /etc/default/timestamp if present. This allows the rootfs to be
read-only / store the file in a persistant location if the whole rootfs
is updated.

(From OE-Core rev: b4de37b7176630d9585b12c50d537cd561c7aeb9)

Signed-off-by: Jeroen Hofstee <jhofstee@victronenergy.com>
Signed-off-by: Richard Purdie <richard.purdie@linuxfoundation.org>

meta/recipes-core/initscripts/initscripts-1.0/bootmisc.sh

@@ -8,7 +8,10 @@
 # Short-Description: Misc and other.
 ### END INIT INFO
 
+TIMESTAMP_FILE=/etc/timestamp
+
 . /etc/default/rcS
+[ -f /etc/default/timestamp ] && . /etc/default/timestamp
 #
 # Put a nologin file in /etc to prevent people from logging in before
 # system startup is complete.
@@ -64,10 +67,10 @@ fi
 # If the timestamp is more recent than the current time,
 # use the timestamp instead.
 test -x /etc/init.d/hwclock.sh && /etc/init.d/hwclock.sh start
-if test -e /etc/timestamp
+if test -e "$TIMESTAMP_FILE"
 then
 	SYSTEMDATE=`date -u +%4Y%2m%2d%2H%2M%2S`
-	read TIMESTAMP < /etc/timestamp
+	read TIMESTAMP < "$TIMESTAMP_FILE"
 	if [ ${TIMESTAMP} -gt $SYSTEMDATE ]; then
 		# format the timestamp as date expects it (2m2d2H2M4Y.2S)
 		TS_YR=${TIMESTAMP%??????????}

meta/recipes-core/initscripts/initscripts-1.0/save-rtc.sh

@@ -9,5 +9,9 @@
 # Description:       
 ### END INIT INFO
 
+TIMESTAMP_FILE=/etc/timestamp
+
+[ -f /etc/default/timestamp ] && . /etc/default/timestamp
+
 # Update the timestamp
-date -u +%4Y%2m%2d%2H%2M%2S 2>/dev/null > /etc/timestamp
+date -u +%4Y%2m%2d%2H%2M%2S 2>/dev/null > "$TIMESTAMP_FILE"