ARM: dts: Add minimal support for dm8168-evm

ARM: dts: Add minimal support for dm8168-evm

This allows booting the device with basic functionality.

Note that at least on my revision c board the DDR3 does
not seem to work properly and only some of the memory
can be reliably used.

Also, the mainline u-boot does not seem to properly
initialize the ethernet, so I've been using the old TI
u-boot at:

http://arago-project.org/git/projects/?p=u-boot-omap3.git;a=summary

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