soong: Add TARGET_LEGACY_HW_DISK_ENCRYPTION conditional

Change-Id: I2c67fe632d415353273839493a86cdd75bd93b23
diff --git a/build/soong/Android.bp b/build/soong/Android.bp
index 6f7bd55..4069921 100644
--- a/build/soong/Android.bp
+++ b/build/soong/Android.bp
@@ -191,6 +191,23 @@
 }
 
 soong_config_module_type {
+    name: "legacy_hw_disk_encryption",
+    module_type: "cc_defaults",
+    config_namespace: "blissQcomVars",
+    bool_variables: ["legacy_hw_disk_encryption"],
+    properties: ["cppflags"],
+}
+
+legacy_hw_disk_encryption {
+    name: "legacy_hw_disk_encryption_defaults",
+    soong_config_variables: {
+        legacy_hw_disk_encryption: {
+            cppflags: ["-DLEGACY_HW_DISK_ENCRYPTION"],
+        },
+    },
+}
+
+soong_config_module_type {
     name: "no_cameraserver",
     module_type: "cc_defaults",
     config_namespace: "blissGlobalVars",