Added beagleboard defconfig overlay

Only supporting beagleboard now for in-house development purposes.
Also removed all the Yocto Project-generated BSP stuff. Not using
Yocto right now, so they are unnecessary.

Signed-off-by: Mike Lewis <mikelewis@alphalem.com>
Removed linux-yocto append file

Using linux-mainline right now since we're working with meta-ti's
beagleboard implementation.

Signed-off-by: Mike Lewis <mikelewis@alphalem.com>
linux-mainline: changes to append file

FILESEXTRAPATHS wasn't working, among other things, according to thread
on [yocto]. Copied the same format another person was using that appears
to work.

Signed-off-by: Mike Lewis <mikelewis@alphalem.com>