n1sdp: Add n1sdp.xml manifest file

This manifest file points to master branch on gitlab for a few
components. There might be untagged changes which have not yet been
fully verified and should be considered unstable until they
are tagged in an official release.

Signed-off-by: sahil <sahil@arm.com>
Change-Id: Ib0d1faab91c5aa801e02c55ee694111c259bc879