shamu: add first_api_level property

Bug: 33343908
Change-Id: Ie193497a45c14ba5f5d41bc052aae81b71dfa8b9
(cherry picked from commit 995714687de8cd742b563935865525d74c7c9a84)
diff --git a/device.mk b/device.mk
index a05b9b8..d933bbe 100644
--- a/device.mk
+++ b/device.mk
@@ -411,3 +411,7 @@
 # OEM Unlock reporting
 ADDITIONAL_DEFAULT_PROPERTIES += \
     ro.oem_unlock_supported=1
+
+# ro.product.first_api_level indicates the first api level the device has commercially launched on.
+PRODUCT_PROPERTY_OVERRIDES += \
+    ro.product.first_api_level=21