dt-bindings: clock: Move exynos-audss-clk.h to dt-bindings/clock

Most of the clock related dt-binding header files are located in
dt-bindings/clock folder. It would be good to keep all the similar
header files at a single location.

Signed-off-by: Tushar Behera <tushar.behera@linaro.org>
Reviewed-by: Sachin Kamat <sachin.kamat@linaro.org>
Acked-by: Tomasz Figa <t.figa@samsung.com>
Signed-off-by: Kukjin Kim <kgene.kim@samsung.com>