warp7: add warp7_auth_or_fail

Doing secure boot on the WaRP7 using a common image format and the same
variable to represent the base address for each call means we can reduce
down the command to a single environment command.

This patch adds warp7_auth_or_fail as a wrapper around
"hab_auth_img_or_fail ${hab_ivt_addr} ${filesize} 0".

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>