[meta-xilinx] Building BOOT.BIN for the zedboard

[Philip Balister]

https://github.com/balister/meta-xilinx/commits/boot-bin-1

This branch will build BOOT.BIN for the zedboard and updates the
zedboard to 2013.07 + the uEnv.txt patch. I had to bump MAXARGS to get
it to boot with the included uEnv.txt file.

Philip