We can now probe devices with device tree only configuration using
ti-sysc interconnect target module driver. Let's configure the
module, but keep the legacy "ti,hwmods" peroperty until the child
devices are probing with ti-sysc interconnect driver.

The display subsystem (DSS) is in a 16MB interconnect target module
mapped to l4 and l3 buses. We are only using the l3 port as recommended
by the TRM. So there is no need to configure l4 ranges like we've done
for l4 ABE instance for example.

Initially let's just update the top level dss node to probe with ti-sysc
interconnect target module driver. The child nodes are still children
of dispc, only the node indentation changes for them now along with
using the reg range provided by top level dss.

Let's also add add a note about using only the l3 access without l4
as noted in the TRM.

Cc: Jyri Sarha <jsarha@ti.com>
Cc: Laurent Pinchart <laurent.pinchart@ideasonboard.com>
Cc: Sebastian Reichel <sre@kernel.org>
Cc: Tomi Valkeinen <tomi.valkeinen@ti.com>
Signed-off-by: Tony Lindgren <tony@atomide.com>