machine-xilinx-board.inc : Add definition of boot files for wic utility.

With this, and the files added to the machine config you can run:

wic create ../oe-core/scripts/lib/image/canned-wks/sdimage-bootpart.wks -e some-image -o images/$MACHINE

and end up with a file you can dd onto an sd card.

Signed-off-by: Philip Balister <philip@balister.org>
Signed-off-by: Nathan Rossi <nathan.rossi@xilinx.com>
zedboard : Add files to support bootable image creation with wic.

Signed-off-by: Philip Balister <philip@balister.org>
Signed-off-by: Nathan Rossi <nathan.rossi@xilinx.com>
zc702 : Add files to support bootable image creation with wic.

Signed-off-by: Philip Balister <philip@balister.org>
Signed-off-by: Nathan Rossi <nathan.rossi@xilinx.com>