ARM: ux500: pass parent pointer to each platform device

This patch provides a means for any device within ux500
platform code to allocate its own parent. This is particularly
prudent with the introduction of /sys/devices/socX, as a
device can now proclaim to be integral part of an SoC, rather
than a more generic platform device. Latter patches make good
use of this functionality.

Signed-off-by: Lee Jones <lee.jones@linaro.org>
Acked-by: Linus Walleij <linus.walleij@linaro.org>
Signed-off-by: Arnd Bergmann <arnd@arndb.de>