ARM: versatile: move restart to the device tree

We have a power/reset driver for the Versatile family
in drivers/power/reset so let's just activate that driver
and use it and get rid of some non-DT remnants.

Cc: Rob Herring <robh@kernel.org>
Signed-off-by: Linus Walleij <linus.walleij@linaro.org>