ARM: dts: Remove L3 compatible value for dm816x

The interconnects on dm816x are like on omap4, so we should use
l3-noc instead of l3-smx. But as the related SoC specific
l3_target_data is still missing from omap_l3_noc let's just
remove the entry for now.

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