Add Android.bp.list and soong.variables to inputs for soong_docs action

While this is not a comprehensive list of all inputs of this action (as the action
depends on all blueprint files in the source tree), this closer to the truth.

Test: Manually verified ninja output, checkbuild approved validation for aosp-crosshatch
Change-Id: I77a0f612afb025232bee7d3ac31257b808991829
diff --git a/cmd/soong_build/main.go b/cmd/soong_build/main.go
index 905f206..532d9e4 100644
--- a/cmd/soong_build/main.go
+++ b/cmd/soong_build/main.go
@@ -59,7 +59,7 @@
 	ctx := android.NewContext()
 	ctx.Register()
 
-	configuration, err := android.NewConfig(srcDir, bootstrap.BuildDir)
+	configuration, err := android.NewConfig(srcDir, bootstrap.BuildDir, bootstrap.ModuleListFile)
 	if err != nil {
 		fmt.Fprintf(os.Stderr, "%s", err)
 		os.Exit(1)