ARM: dts: add audio clock controller for exynos5420

This adds device-tree bindings for the audio subsystem clock controller
on Exynos 5420.

Signed-off-by: Andrew Bresticker <abrestic@chromium.org>
Reviewed-on: https://gerrit.chromium.org/gerrit/57712
Reviewed-by: Simon Glass <sjg@chromium.org>
Signed-off-by: Padmavathi Venna <padma.v@samsung.com>
Signed-off-by: Kukjin Kim <kgene.kim@samsung.com>