infra: update manifest for RD-INFRA-2021.09.17 release

The RD-INFRA-2021.09.17 release refreshes the software stack for all the
supported Neoverse Reference Design platforms. So update the release
tags in the manifest files.

Signed-off-by: Thomas Abraham <thomas.abraham@arm.com>
Change-Id: I22aa555808550afdc063768b7ac27b1dc344da55