ARM: ux500: Remove temporary snowball_of_platform_devs enablement structure

All Device Tree enablement for Snowball's Platform  devices; LEDs, Keys,
Ethernet and all associated AB8500 Multi-Functional Devices are now
complete, so here we remove any trace of adding those devices when Device
Tree is enabled.

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