[U-Boot] [RFC] implementation of generic distro configs

[Dennis Gilmore]

As a followup to http://lists.denx.de/pipermail/u-boot/2013-August/160080.html
ive put together what i Think is a reasonable starting point for defining a
unified set of features and options. 

There are some things that really need some more work yet. mostly to do with
austomatically loading of the dtb.  All of these patches are currently enabled
in Fedora's u-boot builds.

the wandboard in particular has received a lot of testing using sysboot command
to load a extlinux.conf file. which did pick up bugs in teh pxe.c code early on.
I would appreciate some feedback from a wider audience as we move to making this
be a default configuration.

Dennis