[meta-xilinx] Minized support

[Philip Balister]

I finally replaced the provided u-boot with something based of the
version in thud.

Usually issues, no ps7 files source tree and had to enable SPL and
change some settings. I suppose I should go ahead and send those
upstream. Always nice to have the default build work :)

I'm looking at changing the kernel to a fitImge and building a ramdisk
image for qspi. I'd like to boot from qspi, format the emmc and untar a
file system (from usb) into the emmc. Finally boot from a kernel on the
emmc. Does this sound worth upstreaming to meta-xilinx-contrib, or shold
I just carry it locally?

Philip