configs/sgi575: 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: I586e41f4c64f2485a32a719e99cd22665f86892d
Signed-off-by: Thomas Abraham <thomas.abraham@arm.com>