ARM: dts: Add basic clocks for dm816x

The clocks on dm816x are a bit different from the other omap
variants. The clocks are sourced from a FAPLL (Flying Adder PLL)
unlike on other omaps. Other than that, it's a similar setup
to am33xx with extra muxes and dividers that can be defined
as existing component clocks.

Cc: Brian Hutchinson <b.hutchman@gmail.com>
Cc: Paul Walmsley <paul@pwsan.com>
Cc: Tero Kristo <t-kristo@ti.com>
Signed-off-by: Tony Lindgren <tony@atomide.com>