arm/fvp: add recipes for Ecosystem FVPs

Add recipes for the SGI-575 and N1-Edge reference designs from the
Ecosystem FVP collection:

https://developer.arm.com/tools-and-software/open-source-software/arm-platforms-software/arm-ecosystem-fvps



These FVPs are free to download and use.

Change-Id: Ia645e4a7264f73ec42ee61ab2907a9bfdbe7c25d
Signed-off-by: Ross Burton <ross.burton@arm.com>