Scale the flexibility for SVN settings on other devices

Let some devices use it's own SVN for now.

Test: adb shell getprop | grep ro.vendor.build.svn
Bug: 173989803
Bug: 173772608
Change-Id: I5f7f0984653a2bfe8f0693530ed1ed1a83bd28c4
diff --git a/device-common.mk b/device-common.mk
index 83abbb0..b408dcd 100644
--- a/device-common.mk
+++ b/device-common.mk
@@ -837,8 +837,10 @@
 PRODUCT_PACKAGES += $(HIDL_WRAPPER)
 
 # Increment the SVN for any official public releases
+ifeq ($(PRODUCT_DEVICE_SVN_OVERRIDE),)
 PRODUCT_PROPERTY_OVERRIDES += \
 	ro.vendor.build.svn=19
+endif
 
 # Enable iwlan service logging for debug
 ifneq (,$(filter userdebug eng, $(TARGET_BUILD_VARIANT)))