Update Petitboot to v1.9.0 and enable IPv6

Petitboot v1.9.0 includes changes to support IPv6 and DHCPv6. This
depends on IPv6 kernel support and the udhcpc6 client from Busybox.

Signed-off-by: Samuel Mendoza-Jonas <sam@mendozajonas.com>
diff --git a/openpower/configs/busybox.fragment b/openpower/configs/busybox.fragment
index bd81d7b..2c9b176 100644
--- a/openpower/configs/busybox.fragment
+++ b/openpower/configs/busybox.fragment
@@ -3,3 +3,8 @@
 CONFIG_FEATURE_TASKSET_FANCY=y
 CONFIG_FEATURE_PIDFILE=y
 CONFIG_PID_FILE_PATH="/var/run"
+CONFIG_PING6=y
+CONFIG_UDHCPC6=y
+CONFIG_FEATURE_UDHCPC6_RFC3646=y
+CONFIG_FEATURE_UDHCPC6_RFC4704=y
+CONFIG_FEATURE_UDHCPC6_RFC4833=y