Set min_sdk_version to be part of mainline modules

Modules contributing mainline modules (APK/APEX) should set
min_sdk_version as well as apex_available.

For now setting min_sdk_version doesn't change build outputs.
But build-time checks will be added soon.

Bug: 152655956
Test: m
Change-Id: Ifea5ed988fad2e0d29271e6e9cbf0e12100b37d9
diff --git a/libs/gui/sysprop/Android.bp b/libs/gui/sysprop/Android.bp
index e7f7c1f..64b1eac 100644
--- a/libs/gui/sysprop/Android.bp
+++ b/libs/gui/sysprop/Android.bp
@@ -4,4 +4,7 @@
     api_packages: ["android.sysprop"],
     property_owner: "Platform",
     vendor_available: true,
+    cpp: {
+        min_sdk_version: "29",
+    },
 }