This message was posted on behalf of Intel Corporation
Thanks for reaching out!
I understand how you feel, indeed the documentation regarding Galileo's BSP is very out of date. First I would like to let you know that I will make sure to pass your feedback to the appropriate team.
However, if you'd like to build Galileo's Yocto image, I would suggest you to use Quark's X1000 BSP. That BSP is compatible with Galileo since it is the SoC implemented on the board. You will find the BSP and its documentation in https://downloadcenter.intel.com/download/23197/Intel-Quark-SoC-X1000-Board-Support-Package-BSP-. Also, if you'd like to learn even more about Yocto development, you can always check their documentation, I'd suggest you to start by their Mega Manual http://www.yoctoproject.org/docs/1.7.3/mega-manual/mega-manual.html.
I hope this information helps you,