ARM: ux500: Add all encompassing sound node to the Snowball Device Tree

This is where we link together all of the SoC sound components for
a given platform. This all encompassing sound node is only found
in the very lowest hierarchical DTS file, since the component mix may
well change from board variant to board variant.

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