Add display-controller to list of generic node names

The device-tree specification does not present a generic node name for
hardware compositors.  Several names are used, but 'display-controller'
is the most straight-forward name to describe such device.

Signed-off-by: Raphael Gallais-Pou <rgallaispou@gmail.com>
Link: https://lore.kernel.org/r/20250331200224.41184-1-rgallaispou@gmail.com
Signed-off-by: Rob Herring (Arm) <robh@kernel.org>

Author: rgallaispou

source/chapter2-devicetree-basics.rst

@@ -221,6 +221,7 @@ name should be one of the following choices:
    * crypto
    * disk
    * display
+   * display-controller
    * dma-controller
    * dsi
    * dsp