ppc44x: mark as broken

This target has consistently failed builds for a long time and it does
not look like it has any users left, nor any maintainers.

Signed-off-by: Felix Fietkau <nbd@nbd.name>

target/linux/ppc44x/Makefile

@@ -9,7 +9,7 @@ include $(TOPDIR)/rules.mk
 ARCH:=powerpc
 BOARD:=ppc44x
 BOARDNAME:=AMCC/IBM PPC44x
-FEATURES:=squashfs
+FEATURES:=squashfs broken
 CPU_TYPE:=440
 MAINTAINER:=Imre Kaloz <kaloz@openwrt.org>