totalcompute/tc0: update doc for TC0-2021.07.31 release

Updated change-log, release_notes, user-guide for tc0 with new
software/hardware features added and its changes from the previous release.

Signed-off-by: Avinash Mehta <avinash.mehta@arm.com>
Change-Id: I5fe0b836721441861ecad5cdeeab1c0a49c9b99c