dt-bindings: display/panel: Add missing unit names

Some examples were missing the unit names triggering

Warning (unit_address_vs_reg): .../panel: node has a reg or ranges property, but no unit name

warnings when used verbatim in DTs and running dtc with W=1.

Signed-off-by: Guido Günther <[e-mail]>
Signed-off-by: Thierry Reding <[e-mail]>
Link: https://patchwork.freedesktop.org/patch/msgid/[e-mail]

Documentation/devicetree/bindings/display/panel/innolux,p079zca.txt

···
 Example:
 
 	&mipi_dsi {
-		panel {
+		panel@0 {
 			compatible = "innolux,p079zca";
 			reg = <0>;
 			power-supply = <...>;

Documentation/devicetree/bindings/display/panel/innolux,p097pfg.txt

···
 Example:
 
 	&mipi_dsi {
-		panel {
+		panel@0 {
 			compatible = "innolux,p079zca";
 			reg = <0>;
 			avdd-supply = <...>;

Documentation/devicetree/bindings/display/panel/kingdisplay,kd097d04.txt

···
 Example:
 
 	&mipi_dsi {
-		panel {
+		panel@0 {
 			compatible = "kingdisplay,kd097d04";
 			reg = <0>;
 			power-supply = <...>;