Documentation: fix release version linking

Correct links to coreboot release notes and fix related "document
isn't included in any toctree" warnings.

Change-Id: I6563da6f82f5686e54791331312434828c63f5a6
Signed-off-by: Tom Hiller <thrilleratplay@gmail.com>
Reviewed-on: https://review.coreboot.org/27719
Tested-by: build bot (Jenkins) <no-reply@coreboot.org>
Reviewed-by: Martin Roth <martinroth@google.com>
1 file changed