Investigate getting vexpress boards working properly under lava

Vexpress boards have given us problems in the past because of deployment issues, sd booting problems, firmware (hardware monitor) quirks, and more. After talking to our new LT Lead for vexpress today, I learned that many of these problems *should* be recently fixed, and there's a blueprint on the horizon to make sure that Linaro images can work in a more usual way on vexpress. We should revisit this and see if we can get these boards properly working under LAVA now.