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/vr/libpdx/Android.bp b/libs/vr/libpdx/Android.bp
index 23a4224..24ba830 100644
--- a/libs/vr/libpdx/Android.bp
+++ b/libs/vr/libpdx/Android.bp
@@ -2,6 +2,7 @@
     name: "libpdx_headers",
     export_include_dirs: ["private"],
     vendor_available: true,
+    min_sdk_version: "29",
 }
 
 cc_library_static {