[TF-A] TF-A LTS wiki page

Hello team,

After the recent discussion in the tech forums for the need of a LTS release, I have create a wiki page [1] on tf.org to discuss how we should move forward. The page is expected to be a "live" document and the intention is to allow the community to capture current problems and expectations from the LTS version.

Request you to review the page and provide feedback.

Thanks, -Varun

[1] https://developer.trustedfirmware.org/w/tf_a/lts_proposal/