Reformat interrupt tree diagram to be clearer

Refactor the interrupt tree example diagram so that the natural tree
appears above the interrupt tree. The diagram is clearer that way. Also
change the colours and line styles to be clearer.

Signed-off-by: Grant Likely <[email protected]>

Author: glikely

source/devicetree-basics.rst

@@ -836,6 +836,7 @@ sits in the logical interrupt tree.
    subgraph cluster_devices {
       label = "Devicetree"
       graph [ style = dotted ]
+      "soc" [ ]
       "device1" [ label = "device1 | interrupt-parent=\<&open-pic\>" ]
       "device2" [ label = "device2 | interrupt-parent=\<&gpioctrl\>" ]
       "pci-host" [ label = "pci-host | interrupt-parent=\<&open-pic\>" ]
@@ -845,6 +846,7 @@ sits in the logical interrupt tree.
       "gpioctrl" [ label = "gpioctrl | interrupt-parent=\<&open-pic\>" ]
       "device3" [ label = "device3 | interrupt-parent=\<&gpioctrl\>" ]
 
+      edge [dir=back color=blue]
       "soc":e -> "device1":w
       "soc":e -> "device2":w
       "soc":e -> "open-pic":w
@@ -869,18 +871,18 @@ sits in the logical interrupt tree.
       "i-slot0" [ label = "slot0" ]
       "i-slot1" [ label = "slot1" ]
 
-      edge [dir=back color=blue]
-      "i-open-pic" -> "i-device1"
-      "i-open-pic" -> "i-pci-host"
-      "i-open-pic" -> "i-gpioctrl"
-      "i-pci-host" -> "i-slot0"
-      "i-pci-host" -> "i-slot1"
-      "i-gpioctrl" -> "i-device2"
-      "i-gpioctrl" -> "i-device3"
+      edge [dir=back color=green]
+      "i-open-pic":e -> "i-device1":w
+      "i-open-pic":e -> "i-pci-host":w
+      "i-open-pic":e -> "i-gpioctrl":w
+      "i-pci-host":e -> "i-slot0":w
+      "i-pci-host":e -> "i-slot1":w
+      "i-gpioctrl":e -> "i-device2":w
+      "i-gpioctrl":e -> "i-device3":w
    }
 
    subgraph {
-      edge [color="red", constraint=false, dir=forward]
+      edge [color=red, style=dotted, constraint=false]
       "open-pic" -> "i-open-pic"
       "gpioctrl":w -> "i-gpioctrl"
       "pci-host" -> "i-pci-host"