init: add manifest for all supported platforms

Initialize the manifest repo for Neoverse Reference Design platforms.
The manifest of all the supported platforms are included in both
variants - pinned and tracking. The pinned manifests have 'pinned-'
prefixed to the platform name. The tracking manifests do not have any
prefix.

Signed-off-by: Thomas Abraham <thomas.abraham@arm.com>
Change-Id: I12cbe3f5cfcc49ce8c019efdc2d3a0fe3e12c6cd