rdfremont: add a manifest for RD-Fremont platforms

Add manifest for RD-Fremont and RD-Fremont-Cfg1 platforms. Both the
pinned and un-pinned versions of manifest is added. The un-pinned
version of the manifest allows updates on the development branch
to be used.

Signed-off-by: Vijayenthiran Subramaniam <vijayenthiran.subramaniam@arm.com>
Change-Id: Ibb1b896c6bb0752d01c07a8c51d22b429973653f