[meta-xilinx] adding patch file for u-boot

[Richard Cagley]

> Ok, so to clear some confusion 'u-boot-spl-xlnx' is intended to build
> just u-boot-spl sourcing the "ps7_init.c/h" from a separate recipe (so
> dependencies work and prevent users from creating useless non-working
> u-boot-spl binaries). e.g. fsbl-platform-init.bb which provides the
> ps7_init.c/h for zc702, zc706, etc. or platform-init.bb which is an
> example for how you can provide ps7_init.c/h from your layer
> (bbappending this recipe is ok to).
>
> Depending on what you are trying to do you will need to provide a
> ps7_init.c/h for your machine 'trenz-zynq7' in order to build
> u-boot-spl-xlnx. If you are not after u-boot-spl for your platform
> (e.g. you are using FSBL) then you can ignore the u-boot-spl-xlnx
> recipe and apply any patches for 'u-boot' to the 'u-boot-xlnx' recipe
> only. Otherwise apply your patches to both recipes.
>
> Regards,
> Nathan

Nathan,
oh, now I see the pattern with how the picozed was added. You got me
one step closer ;)
But now I'm getting a do_install failure on u-boot-spl-xlnx as it
can't find boot.bin. And, for u-boot-xlnx it's complaining about
missing u-boot-dtb.img

I have the below in my platform-init.bbappend. Any chance you have an
idea what i'm missing?

FILESEXTRAPATHS_prepend := "${THISDIR}/platform-init/trenz-zynq7:"
COMPATIBLE_MACHINE_trenz-zynq7 = "trenz-zynq7"