linux-yocto: introduce v6.1 reference kernel recipes

6.1 is a LTS kernel, and our next reference kernel. Some new
features like rust support are not directly used, but will
be available to start testing.

Signed-off-by: Bruce Ashfield <bruce.ashfield@gmail.com>
Signed-off-by: Richard Purdie <richard.purdie@linuxfoundation.org>