Mark libpiex vendor_available.

libpiex 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

Merged-In: Ic5bba201b52abe6ab985fabcb04811f97cd9cae5
Change-Id: I33f9c4bf15a33d5792cbe617420a1c48baf492e6
(cherry picked from commit 666035422526cc47f047664c9587ea631d419620)
diff --git a/Android.bp b/Android.bp
index 894bf3b..f4a2e98 100644
--- a/Android.bp
+++ b/Android.bp
@@ -27,6 +27,7 @@
 
 cc_library_shared {
     name: "libpiex",
+    vendor_available: true,
     srcs: [
         "src/tiff_parser.cc",
         "src/piex.cc",