added more explaination of contents of boot.bin
make relative path to access the dtc tool (which means that the
2 projects 'device_xilinx_kernel' and 'zync_boot' must be siblings
in the directory tree.)
updated typo for zc702.  Also made MAC address different from zedboard.

(why is the diff between the 2 dts files still so large? ... jca)