Mark libdiskconfig vendor_available.

libdisckonfig is a library which belongs to vndk-cap. Mark it
vendor_available to enable vndk abi stability checks on it.

Details: https://android-review.googlesource.com/368372

Test: mm -j64

Bug: 38244611

Change-Id: I079869f0120fa33893540b72044ddf25c1d04bf2
diff --git a/libdiskconfig/Android.bp b/libdiskconfig/Android.bp
index 041fd63..088981a 100644
--- a/libdiskconfig/Android.bp
+++ b/libdiskconfig/Android.bp
@@ -1,5 +1,6 @@
 cc_library {
     name: "libdiskconfig",
+    vendor_available: true,
     srcs: [
         "diskconfig.c",
         "diskutils.c",