Expose TargetFSConfigGen to DeviceConfig from Make

Bug: 118089258
Test: m oemaids_header_gen oemaids_headers
Change-Id: I2675822ae01af9bbec70f0c0413c047f36b5e024
Merged-In: I2675822ae01af9bbec70f0c0413c047f36b5e024
(cherry picked from commit 71c74607133b017c874340c0cce6892a14733b50)
diff --git a/android/variable.go b/android/variable.go
index 56ca666..7daa926 100644
--- a/android/variable.go
+++ b/android/variable.go
@@ -281,6 +281,8 @@
 	ProductHiddenAPIStubs       []string `json:",omitempty"`
 	ProductHiddenAPIStubsSystem []string `json:",omitempty"`
 	ProductHiddenAPIStubsTest   []string `json:",omitempty"`
+
+	TargetFSConfigGen *string `json:",omitempty"`
 }
 
 func boolPtr(v bool) *bool {