ARM: ux500: Remove unused snowball_of_platform_devs struct

This was left over during a recent clean-up which removed Device Tree
helper structs. There is no longer a requirement for it, so we can just
remove it.

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