ARM: dts: turris-omnia: add LED controller node

ARM: dts: turris-omnia: add LED controller node

Linux now has incomplete support for the LED controller on Turris Omnia:
it can set brightness and colors for each LED.

The controller can also put these LEDs into HW controlled mode, in which
the LEDs are controlled by HW: for example the WAN LED is connected via
MCU to the WAN PHY LED pin.

The driver does not support these HW controlled modes yet, and on probe
puts the LEDs into SW controlled mode.

Add node describing the LED controller, but disable it for now.

Signed-off-by: Marek Behún <kabel@kernel.org>
Cc: linux-arm-kernel@lists.infradead.org
Cc: Uwe Kleine-König <uwe@kleine-koenig.org>
Cc: Jason Cooper <jason@lakedaemon.net>
Cc: Gregory CLEMENT <gregory.clement@bootlin.com>
Cc: Andreas Färber <afaerber@suse.de>
Cc: Rob Herring <robh+dt@kernel.org>
Cc: devicetree@vger.kernel.org
Signed-off-by: Gregory CLEMENT <gregory.clement@bootlin.com>