Mark libsuspend vendor_available.

libsuspend 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: I2243c6d8710b6b2f80375849e82afba28a735507
diff --git a/libsuspend/Android.bp b/libsuspend/Android.bp
index d27ceea..7883151 100644
--- a/libsuspend/Android.bp
+++ b/libsuspend/Android.bp
@@ -2,6 +2,8 @@
 
 cc_library {
     name: "libsuspend",
+    vendor_available: true,
+
     srcs: [
         "autosuspend.c",
         "autosuspend_autosleep.c",