ARM: dts: Add basic dm816x device tree configuration

Similar to other omap variants, let's add dm816x support.

Note that this is based on generated data from the
TI81XX-LINUX-PSP-04.04.00.02 patches published at:

http://downloads.ti.com/dsps/dsps_public_sw/psp/LinuxPSP/TI81XX_04_04/04_04_00_02/index_FDS.html

I've verified the basic functionality, but have not been
able to test all the devices on dm8168-evm.

Cc: Brian Hutchinson <b.hutchman@gmail.com>
Signed-off-by: Tony Lindgren <tony@atomide.com>