openrisc: Updates after openrisc.net has been lost

The openrisc.net domain expired and was taken over by squatters.
These updates point documentation to the new domain, mailing lists
and git repos.

Also, Jonas is not the main maintainer anylonger, he reviews changes
but does not maintain a repo or sent pull requests.  Updating this to
add Stafford and Stefan who are the active maintainers.

Acked-by: Olof Kindgren <olof.kindgren@gmail.com>
Signed-off-by: Stafford Horne <shorne@gmail.com>