Announce 11.2-BETA1 is available.
Fix the link for the GUMSTIX image, and comment it as the build
failed.
Comment the BANANAPI link, there was an issue with the image.
Activate the download URLs for 11.2.
Update the releng page to reflect stable/11 is frozen (belatedly).

Approved by: re (implicit)
Sponsored by: The FreeBSD Foundation