Migrate khrplatform.h to ndk_headers.

Test: make native
Bug: http://b/30465923
Change-Id: Idaf0eb973b7569f92b1f1575869d13b8c5e706fd
diff --git a/opengl/Android.bp b/opengl/Android.bp
index 3deb9f0..164be20 100644
--- a/opengl/Android.bp
+++ b/opengl/Android.bp
@@ -40,6 +40,13 @@
     srcs: ["include/GLES3/**/*.h"],
 }
 
+ndk_headers {
+    name: "khr_headers",
+    from: "include",
+    to: "",
+    srcs: ["include/KHR/**/*.h"],
+}
+
 subdirs = [
     "*",
 ]