ARM: dts: Move dra7 l3 noc to a separate node

In order to prepare for probing l3 with genpd, we need to move l3 noc
into a separate node for l3 interconnect to have it's own regs, and
to avoid it claiming more than it needs for the io regions.

Tested-by: Kishon Vijay Abraham I <kishon@ti.com>
Signed-off-by: Tony Lindgren <tony@atomide.com>