tools: add kwboot binary to .gitignore file

Signed-off-by: Luka Perkov <uboot@lukaperkov.net>
Acked-by: Prafulla Wadaskar <Prafulla@marvell.com>
Acked-by: Mike Frysinger <vapier@gentoo.org>

tools/.gitignore

@@ -2,6 +2,7 @@
 /envcrc
 /gen_eth_addr
 /img2srec
+/kwboot
 /mkenvimage
 /mkimage
 /mpc86x_clk