Unless explicitely overridden, PKGARCH defaults to $(ARCH)_$(CPU_TYPE). The ar71xx target declaresARCH:=mips and CPU_TYPE:=24kc and no explicit ARCH_PACKAGES so it will expect packages to belong to the mips_24kc architecture.
MIPS74 processors found in some AR71XX chips (but not most) are backward compatible to run MIPS24 code, so everything is compiled for 24. However the "el" version means little-endian which is not compatible with the non "el" big endian.
That's interesting!
But it sounds weird to me that a little endian architecture has a "specialized" version, while the big endian one relies on backwards compatibility!
Thanks.
There was discussion on the mailing list about it a while back, it kind of boiled down to the gains for using 74kc optimisations being minimal compared to 24kc on ar71xx.