fadump: leverage kernel support to re-regisgter FADump

With kernel commit 0823c68b054b ("powerpc/fadump: re-register firmware-
assisted dump if already registered") support is enabled to re-register
when FADump is alredy registered. Leverage that option in kdump scripts.

Signed-off-by: Hari Bathini <hbathini@linux.ibm.com>
Acked-by: Kairui Song <kasong@redhat.com>

kdumpctl

@@ -1047,7 +1047,8 @@ reload()
 	fi
 
 	if [ $DEFAULT_DUMP_MODE == "fadump" ]; then
-		stop_fadump
+		reload_fadump
+		return $?
 	else
 		stop_kdump
 	fi
@@ -1103,6 +1104,26 @@ stop_kdump()
 	return 0
 }
 
+reload_fadump()
+{
+	echo 1 > $FADUMP_REGISTER_SYS_NODE
+	if [ $? == 0 ]; then
+		echo "fadump: re-registered successfully"
+		return 0
+	else
+		# FADump could fail on older kernel where re-register
+		# support is not enabled. Try stop/start from userspace
+		# to handle such scenario.
+		stop_fadump
+		if [ $? == 0 ]; then
+			start_fadump
+			return $?
+		fi
+	fi
+
+	return 1
+}
+
 stop()
 {
 	if [ $DEFAULT_DUMP_MODE == "fadump" ]; then