Update linkerconfig configuration format

Update linkerconfig configuration format as json.

Bug: 169634881
Test: cuttelfish boot succeeded
Change-Id: Ie95bc961e3b616acb33fc86025950d1c5ba7fd8b
diff --git a/apex/Android.bp b/apex/Android.bp
index ef296d6..80e751c 100644
--- a/apex/Android.bp
+++ b/apex/Android.bp
@@ -64,10 +64,9 @@
     ],
 }
 
-prebuilt_etc {
+linker_config {
     name: "media-linker-config",
-    src: "linker.config.txt",
-    filename: "linker.config.txt",
+    src: "linker.config.json",
     installable: false,
 }