docs: Fix dual-BOOM-single-Rocket documentation

There were two problems here:
    1. The docs indicated that this should be a dual-BOOM and
       single-Rocket config, but the config actually had two Rocket
       cores.
    2. Since the doc include string was 'DualBoomAndRocket', it was
       accidentally matching against the 'DualBoomAndRocketOneHwacha'
       section, which comes first in the file.

So, I created a new 'DualLargeBoomAndSingleRocketConfig' config which
only has one Rocket core, and changed the doc include string to
'DualBoomAndSingleRocket'.

docs/Customization/Heterogeneous-SoCs.rst

@@ -17,8 +17,8 @@ The following example shows a dual core BOOM with a single core Rocket.
 
 .. literalinclude:: ../../generators/chipyard/src/main/scala/config/HeteroConfigs.scala
     :language: scala
-    :start-after: DOC include start: DualBoomAndRocket
-    :end-before: DOC include end: DualBoomAndRocket
+    :start-after: DOC include start: DualBoomAndSingleRocket
+    :end-before: DOC include end: DualBoomAndSingleRocket
 
 
 Adding Hwachas

generators/chipyard/src/main/scala/config/HeteroConfigs.scala

@@ -31,12 +31,17 @@ class LargeBoomAndHwachaRocketConfig extends Config(
 // DOC include end: DualBoomAndRocketOneHwacha
 
 
-// DOC include start: DualBoomAndRocket
 class DualLargeBoomAndDualRocketConfig extends Config(
   new boom.common.WithNLargeBooms(2) ++                   // add 2 boom cores
   new freechips.rocketchip.subsystem.WithNBigCores(2) ++  // add 2 rocket cores
   new chipyard.config.AbstractConfig)
-// DOC include end: DualBoomAndRocket
+
+// DOC include start: DualBoomAndSingleRocket
+class DualLargeBoomAndSingleRocketConfig extends Config(
+  new boom.common.WithNLargeBooms(2) ++                   // add 2 boom cores
+  new freechips.rocketchip.subsystem.WithNBigCores(1) ++  // add 1 rocket core
+  new chipyard.config.AbstractConfig)
+// DOC include end: DualBoomAndSingleRocket
 
 class LargeBoomAndRocketWithControlCoreConfig extends Config(
   new freechips.rocketchip.subsystem.WithNSmallCores(1) ++ // Add a small "control" core