u-boot-xlnx.inc: Add support for building working SPL

You need to add the files ps7_init.[ch] via a board specific
SRC_URI append. The ps7 files should be GPL licensed to avoid
license headaches.

Signed-off-by: Philip Balister <philip@balister.org>
Signed-off-by: Nathan Rossi <nathan.rossi@xilinx.com>
u-boot-xlnx: Add support for building SPL for the zc702.

The ps7_init files are GPL versions from:
https://github.com/Xilinx/embeddedsw/tree/master/lib/sw_apps/zynq_fsbl/misc/zc702

I had to edit the .h filename in the .c file. Another option is use the
file names as is, but this needs a patch to u-boot so it looks for
ps7_init_gpl.c.

Signed-off-by: Philip Balister <philip@balister.org>
Signed-off-by: Nathan Rossi <nathan.rossi@xilinx.com>