clk: samsung: Add missing exynos5420 audio related clocks

This patch adds missing definitions of mux clocks required for using
EPLL as the audio subsystem root clock on exynos5420/exynos5422 SoCs.

Reviewed-by: Krzysztof Kozlowski <krzk@kernel.org>
Reviewed-by: Chanwoo Choi <cw00.choi@samsung.com>
Tested-by: Chanwoo Choi <cw00.choi@samsung.com>
Signed-off-by: Sylwester Nawrocki <s.nawrocki@samsung.com>