Move the adb auth code into its own file.

Change-Id: I84cf0bd7777f0147119e7c6afc4096c2e93156a2
diff --git a/adb/adb_auth.h b/adb/adb_auth.h
index b718b42..4431b5b 100644
--- a/adb/adb_auth.h
+++ b/adb/adb_auth.h
@@ -26,6 +26,8 @@
 void adb_auth_verified(atransport *t);
 
 void send_auth_request(atransport *t);
+void send_auth_response(uint8_t *token, size_t token_size, atransport *t);
+void send_auth_publickey(atransport *t);
 
 /* AUTH packets first argument */
 /* Request */