rdv3r1*: add a manifest for RD-V3-R1 platforms

Add manifest for RD-V3-R1 and RD-V3-R1-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.

Change-Id: Ia03d31adbb706fd015b3f617853b11bd2df0bd14
Signed-off-by: Vijayenthiran Subramaniam <vijayenthiran.subramaniam@arm.com>