infra: update the documentation for RD-INFRA-2022.03.31 release

The RD-INFRA-2022.03.31 release updates the software stack for RD-N2,
RD-N2-Cfg1, RD-N2-Cfg1 and RD-Edmunds reference designs. Update the
documentation for these platforms and add a release note for this release.

Signed-off-by: Thomas Abraham <thomas.abraham@arm.com>
Change-Id: I81a2fbee880b5cddfb2108f148a12abd4b26407e