Add support for arm Foundation ARMv8 FVP simulator

Add recipes and configuration files to add Yocto support
for Foundation armv8 simulator from arm.
The following components are supported:
- trusted-firmware-a
- linux kernel (with specific kernel configuration)
- xen (with meta-virtualization layer)
- unpacking and starting the generated image directly in Foundation
simulator (package must be download from www.arm.com website and put in
the directory downloads/licensed/silver.arm.com).

After building, the following command can be used to start a generated
image in foundation:
./tmp/deploy/tools/start-foundation-armv8.sh

Change-Id: Iade343c38f0799ee8523434d555cb3ca42068a86
Signed-off-by: Bertrand Marquis <bertrand.marquis@arm.com>