Define ro.board.first_api_level property

When a device define BOARD_SHIPPING_API_LEVEL with an API level, it
sets a vendor property ro.board.first_api_level in vendor/build.prop.
This is for the GRF devices. Non-GRF devices must not define this
property.

Bug: 176950752
Test: getprop ro.board.first_api_level
Change-Id: I6921d7fe6acca3f73a5fd0fbaa3d4f1e9394541b
diff --git a/core/main.mk b/core/main.mk
index 63fac43..e2dde2d 100644
--- a/core/main.mk
+++ b/core/main.mk
@@ -290,6 +290,13 @@
     ro.product.first_api_level=$(PRODUCT_SHIPPING_API_LEVEL)
 endif
 
+# Vendors with GRF must define BOARD_SHIPPING_API_LEVEL for the vendor API level.
+# This must not be defined for the non-GRF devices.
+ifdef BOARD_SHIPPING_API_LEVEL
+ADDITIONAL_VENDOR_PROPERTIES += \
+    ro.board.first_api_level=$(BOARD_SHIPPING_API_LEVEL)
+endif
+
 ADDITIONAL_VENDOR_PROPERTIES += \
     ro.vendor.build.security_patch=$(VENDOR_SECURITY_PATCH) \
     ro.product.board=$(TARGET_BOOTLOADER_BOARD_NAME) \