doc: Add table of component versions and repository links

Create variables for the version of each component as well as
definitions for the versions and corresponding repository URLs. Add a
table to the top of the components page with the component name, version
used and a repository link.

Issue-Id: SCM-5314
Signed-off-by: Peter Hoyes <Peter.Hoyes@arm.com>
Change-Id: I853c8ea9ee037612a7f1dae2aefffb23930a8961