CLK: TI: Add DPLL clock support

The OMAP clock driver now supports DPLL clock type. This patch also
adds support for DT DPLL nodes.

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