warp7: Define the name of a signed boot-script file

We need to know the name of a signed boot-script, its better to have a
separate variable for this then to simply append some fixed string to an
existing image name.

Signed-off-by: Bryan O'Donoghue <bryan.odonoghue@linaro.org>
Tested-by: Breno Lima <breno.lima@nxp.com>
Reviewed-by: Fabio Estevam <fabio.estevam@nxp.com>

include/configs/warp7.h

@@ -33,6 +33,7 @@
 #define CONFIG_EXTRA_ENV_SETTINGS \
 	CONFIG_DFU_ENV_SETTINGS \
 	"script=boot.scr\0" \
+	"script_signed=boot.scr.imx-signed\0" \
 	"image=zImage\0" \
 	"console=ttymxc0\0" \
 	"ethact=usb_ether\0" \