ARM: ux500: Initial support for PM domains

The ux500 SoC uses the generic PM domain and requires the domains to be
specified through DT.

Currently the genpd callbacks for handling power gating|ungating are
implemented as dummy functions. To be able to enable those to perform
PM domain gating/ungating, each device that resides in the VAPE domain
must be properly handled from a runtime PM perspective.

Signed-off-by: Ulf Hansson <ulf.hansson@linaro.org>
Signed-off-by: Linus Walleij <linus.walleij@linaro.org>