clk: ti: move generic OMAP DPLL implementation under drivers/clk

clk: ti: move generic OMAP DPLL implementation under drivers/clk

With the legacy clock data now gone, we can start moving OMAP clock
type implementations under clock driver. Start this with moving the
generic OMAP DPLL clock type under TI clock driver.

Signed-off-by: Tero Kristo <t-kristo@ti.com>