[PATCH] Makefile: fix mixed implicit and normal rules

[Alexander Aring]

Hi,

i am not a make expert but this is a common error with newer make
versions.

But I think this solution isn't correct. It's better to split in two
rules like:

images/%.s: barebox.bin FORCE
        $(Q)$(MAKE) $(build)=images $@

images: barebox.bin FORCE
        $(Q)$(MAKE) $(build)=images $@

Getting this information from:
http://www.linuxquestions.org/questions/linux-software-2/error-mixed-implicit-and-normal-rules-while-trying-to-build-busybox-826795/

Regards
Alex