docs/BOOT.tftp: Update KC705 boot documentation
docs/BOOT.tftp: Update KC705 boot documentation

Documentation update for KC705

Signed-off-by: Manjukumar Matha <4c64a17569570cb9f1048973bce031c402b55312@xilinx.com>
Signed-off-by: Nathan Rossi <2e8aa918660411855c6d44d5bb2da677aa033255@nathanrossi.com>

Xilinx/meta-xilinx,nathanrossi/meta-xilinx,Xilinx/meta-xilinx,nathanrossi/meta-xilinx,Xilinx/meta-xilinx,nathanrossi/meta-xilinx,Xilinx/meta-xilinx,nathanrossi/meta-xilinx,Xilinx/meta-xilinx,Xilinx/meta-xilinx