Mark libexif as double_loadable

libexif is a VNDK lib and also used indirectly by LLNDK(libmediandk)
which means this lib can be double-loaded.
(deps: libmediandk -> libmedia_jni -> libexif)

Bug: 121280180
Test: m -j
Change-Id: I00a06c43239b6fb5305a9bcc8dd61eb7ca8d1ae4
diff --git a/Android.bp b/Android.bp
index 62ba943..2bd9b88 100644
--- a/Android.bp
+++ b/Android.bp
@@ -22,6 +22,7 @@
     vndk: {
         enabled: true,
     },
+    double_loadable: true,
 
     srcs: [
         "libexif/exif-byte-order.c",