lynx: Use build_flags for SVN

Flag: build.RELEASE_SVN_LYNX
Bug: 332726030
(cherry picked from https://googleplex-android-review.googlesource.com/q/commit:a6d2650cbf619521a78364321a84489ec7acdae4)
Merged-In: Id2c31d9b6b8db9d7948a7a1174be141e3b913171
Change-Id: Id2c31d9b6b8db9d7948a7a1174be141e3b913171

device-lynx.mk

@@ -211,8 +211,15 @@ PRODUCT_VENDOR_PROPERTIES += \
 	vendor.zram.size=3g
 
 # Increment the SVN for any official public releases
+ifdef RELEASE_SVN_LYNX
+TARGET_SVN ?= $(RELEASE_SVN_LYNX)
+else
+# Set this for older releases that don't use build flag
+TARGET_SVN ?= 44
+endif
+
 PRODUCT_VENDOR_PROPERTIES += \
-    ro.vendor.build.svn=44
+    ro.vendor.build.svn=$(TARGET_SVN)
 
 # Set support hide display cutout feature
 PRODUCT_PRODUCT_PROPERTIES += \