n1sdp: Reintroduce tf-l3 and scp boot tests

Commit 83ee9b348ca609e75fbc87b0b8d37372fad81d99 disabled
Platform CI tests for N1SDP because of a major change
in the boot flow.

This patch updates the scripts to adhere to the
newly introduced TBBR based boot flow, and re-enable the
boot tests.

Signed-off-by: sahil <sahil@arm.com>
Change-Id: I7cb8da4e1ff3c48784cbe7a3fabf7c4f688063af
6 files changed