zc706-zynq7: Fix up URLs in the comments

Signed-off-by: Nathan Rossi <nathan.rossi@xilinx.com>
u-boot-xlnx : Add uEnv.txt for zc702 so it boots from SD card.

Signed-off-by: Philip Balister <philip@balister.org>
layer.conf: correct BBFILES append

Due to immediate expansion operator being  used to assign
BBFILES variable, bitbake was ignoring BBFILE_COLLECTIONS.split()
based append to BBFILES used in other layers to add layer specific
bbappends. Use append operator instead of immediate expansion to
correct this.

Signed-off-by: Yasir-Khan <yasir_khan@mentor.com>