soong_config: Add BOOTLOADER_MESSAGE_OFFSET

* libbootloader_message now uses Android.bp

Change-Id: I750a04be97dbe01564d45cd605744b15f209e408
diff --git a/build/soong/android/variable.go b/build/soong/android/variable.go
index 5a6aa8c..029a518 100644
--- a/build/soong/android/variable.go
+++ b/build/soong/android/variable.go
@@ -6,6 +6,9 @@
 	Apply_msm8974_1440p_egl_workaround struct {
 		Cflags []string
 	}
+	Bootloader_message_offset struct {
+		Cflags []string
+	}
 	Has_legacy_camera_hal1 struct {
 		Cflags []string
 	}
@@ -47,6 +50,7 @@
 type ProductVariables struct {
 	Additional_gralloc_10_usage_bits  *string `json:",omitempty"`
 	Apply_msm8974_1440p_egl_workaround  *bool `json:",omitempty"`
+	Bootloader_message_offset  *int `json:",omitempty"`
 	Has_legacy_camera_hal1  *bool `json:",omitempty"`
 	Java_Source_Overlays *string `json:",omitempty"`
 	Should_skip_waiting_for_qsee  *bool `json:",omitempty"`