buildroot: powerpc-utils: Bump version to 1.3.4

This includes a bump to powerpc-utils so we get the latest ppc64_cpu,
which contains a fix so that ppc64_cpu works when CPU hotplug is
disabled in the kernel.

Signed-off-by: Joel Stanley <joel@jms.id.au>
diff --git a/buildroot b/buildroot
index 08caaab..319c6e1 160000
--- a/buildroot
+++ b/buildroot
@@ -1 +1 @@
-Subproject commit 08caaab7192f2a79a5857bab6f8c4f981ff09f37
+Subproject commit 319c6e1453808040f828e49e09c33c2a5bb0d958