infra/rdn2: update manifests for RD-INFRA-2021.05.27 release

For the RD-INFRA-2021.05.27 release, update the RD-N2 and RD-N2-Cfg1
platform manifest. For this release, two unused repos have been removed
from the list. The release tag for the component repos has been updated.

Signed-off-by: Thomas Abraham <thomas.abraham@arm.com>
Change-Id: I77ad2137f698e36e254064d3f6d885ee3304e2a0