ARM: dts: dm816x: add clkctrl nodes

Add clkctrl nodes for DM816x SoC. These are going to be acting as
replacement for part of the existing clock data and the existing
clkctrl hooks under hwmod data.

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