arm-bsp: add support to cortex-a5 designstart

Add tf-a recipes, u-boot, machine configuration, and documentation to
support Arm Cortex-A5 Designstart.

The output of this build is compatible to run on the FVP and
the FPGA implementation of the package.

For more information see:
https://community.arm.com/developer/ip-products/processors/\


designstart/b/blog/posts/\
pre-silicon-software-development-with-arm-models-for-cortex-a5-designstart

Change-Id: Ie2715ad1871975cb7620d7a195c8dd74144629da
Signed-off-by: Rui Miguel Silva <rui.silva@arm.com>
Signed-off-by: Jon Mason <jon.mason@arm.com>