clk: exynos-audss: add support for Exynos 5420

The AudioSS block on Exynos 5420 has an additional clock gate for the
ADMA bus clock.

Signed-off-by: Andrew Bresticker <abrestic@chromium.org>
Acked-by: Mike Turquette <mturquette@linaro.org>
Acked-by: Kukjin Kim <kgene.kim@samsung.com>
Signed-off-by: Tomasz Figa <t.figa@samsung.com>