ARM: ux500: Stop requesting the SoC device to play 'parent' role

There are no more devices which require left to register which require
a parent. This is part of the ux500 conversion over to Device Tree only
booting.

Signed-off-by: Lee Jones <lee.jones@linaro.org>
Signed-off-by: Linus Walleij <linus.walleij@linaro.org>