Autogenerate a soong module to build odm.img

Test: With https://r.android.com/3326400, notice files are the only
diffs for AOSP CF odm.img
Bug: 376755916

Change-Id: I847f0dc8317d9693de39fed19aeac4e7f8a70152
diff --git a/android/config.go b/android/config.go
index 8c4b5cd..616385a 100644
--- a/android/config.go
+++ b/android/config.go
@@ -1549,6 +1549,10 @@
 	return "odm"
 }
 
+func (c *deviceConfig) BuildingOdmImage() bool {
+	return proptools.Bool(c.config.productVariables.BuildingOdmImage)
+}
+
 func (c *deviceConfig) ProductPath() string {
 	if c.config.productVariables.ProductPath != nil {
 		return *c.config.productVariables.ProductPath