ARM: dts: Add clocks for dm814x ADPLL

These use the standard clock bindings and now we can make some
of the fixed clocks into real clocks.

Note that the clock output names may become optional as we
probably want to eventually use descriptive names, or use
just dynamically generated names as suggested by Tero.

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