Add device-tree support for the l3-noc driver.

Use platform_driver_register to defer the probing at device init
time.

Add documentation for the l3-noc bindings.
Signed-off-by: Benoit Cousson <b-cousson@ti.com>
Cc: Tony Lindgren <tony@atomide.com>
Cc: Santosh Shilimkar <santosh.shilimkar@ti.com>