meta: Add explict branch to git SRC_URIs

There is uncertainty about the default branch name in git going forward.
To try and cover the different possible outcomes, add branch names to all
git:// and gitsm:// SRC_URI entries.

This update was made with the script added to contrib in this patch which
aims to help others convert other layers.

Signed-off-by: Richard Purdie <richard.purdie@linuxfoundation.org>