ARM: dts: dm816x: Add an empty chosen node to top level DTSI

Commit 06bfb9c1 ("ARM: dts: dm816x: Remove skeleton.dtsi usage")
removed the skeleton.dtsi usage since we want to get rid of it.

But this can cause issues when booting a kernel with a boot-loader
that doesn't create a chosen node if this isn't present in the DTB
since the decompressor relies on a pre-existing chosen node to be
available to insert the command line and merge other ATAGS info.

Fixes: 06bfb9c1 ("ARM: dts: dm816x: Remove skeleton.dtsi usage")
Reported-by: Pali Rohar <pali.rohar@gmail.com>
Signed-off-by: Javier Martinez Canillas <javier@osg.samsung.com>
Signed-off-by: Tony Lindgren <tony@atomide.com>