configs/rdn1edge: adapt to changes in edk2-platforms

There are changes in edk2-platforms which requires each of the platform
to have its own platform description file. Adapt to these changes
in edk2-platforms repo.

Change-Id: Id6f0a101d460b2f3200575e2728a481f05a286af
Signed-off-by: Thomas Abraham <thomas.abraham@arm.com>