docs: Update www.raspberrypi.com documentation links
docs: Update www.raspberrypi.com documentation links

www.raspberrypi.com restructured its documentation. Reflect the new
links in our docs.

Fixes #954

Signed-off-by: Andrei Gherzan <0401b4310c02ae595fc6a2b84ead073cab9b0442@huawei.com>

agherzan/meta-raspberrypi,agherzan/meta-raspberrypi,agherzan/meta-raspberrypi,agherzan/meta-raspberrypi,agherzan/meta-raspberrypi,agherzan/meta-raspberrypi