Add support for arm Juno Development Board

Add Yocto support for Juno development board:
- add machine definition
- add kernel configuration
- add u-boot patch to get the environment from a file in flash
- add trusted firmware extension to produce a firmware image
- add ifupdown interfaces to start eth0 and eth1 on startup

Change-Id: I5046166cf1cc9e80a57815ef6bfb0cbb263a704e
Signed-off-by: Bertrand Marquis <bertrand.marquis@arm.com>