clk: ti: composite: add support for legacy composite clock init

Legacy clock data is initialized slightly differently compared to
DT clocks, thus add support for this.

Signed-off-by: Tero Kristo <t-kristo@ti.com>
Acked-by: Tony Lindgren <tony@atomide.com>
Signed-off-by: Michael Turquette <mturquette@linaro.org>