[U-Boot] implementation of generic distro options

[Dennis Gilmore]

In this set of patches I am adding a generic set of config options for Distros
to work with. this enables for simplified support of systems by distros.

I have left out any implementations in this set of patches. I am working to redo
all the implementations based on the work done by Stephen Warren in his recent set
to base on top of these and his exists work.

Dennis