ci: add license/metadata for aarch64 gn prebuilt

gn prebuilt was updated in change [1] but missed METADATA and LICENSE
files additions.
Fix the version to the commit hash used for generating the gn tool [2].

[1] https://review.trustedfirmware.org/c/hafnium/prebuilts/+/11612
[2] https://gn.googlesource.com/gn/+/0d00acaef051e63969f936be5dc06ff7aac7213b

Signed-off-by: Olivier Deprez <olivier.deprez@arm.com>
Change-Id: I0209ba32b2f2154255857ffd2484e832c0eb1e99
diff --git a/linux-aarch64/gn/LICENSE b/linux-aarch64/gn/LICENSE
new file mode 100644
index 0000000..a32e00c
--- /dev/null
+++ b/linux-aarch64/gn/LICENSE
@@ -0,0 +1,27 @@
+// Copyright 2015 The Chromium Authors. All rights reserved.
+//
+// Redistribution and use in source and binary forms, with or without
+// modification, are permitted provided that the following conditions are
+// met:
+//
+//    * Redistributions of source code must retain the above copyright
+// notice, this list of conditions and the following disclaimer.
+//    * Redistributions in binary form must reproduce the above
+// copyright notice, this list of conditions and the following disclaimer
+// in the documentation and/or other materials provided with the
+// distribution.
+//    * Neither the name of Google Inc. nor the names of its
+// contributors may be used to endorse or promote products derived from
+// this software without specific prior written permission.
+//
+// THIS SOFTWARE IS PROVIDED BY THE COPYRIGHT HOLDERS AND CONTRIBUTORS
+// "AS IS" AND ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT
+// LIMITED TO, THE IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR
+// A PARTICULAR PURPOSE ARE DISCLAIMED. IN NO EVENT SHALL THE COPYRIGHT
+// OWNER OR CONTRIBUTORS BE LIABLE FOR ANY DIRECT, INDIRECT, INCIDENTAL,
+// SPECIAL, EXEMPLARY, OR CONSEQUENTIAL DAMAGES (INCLUDING, BUT NOT
+// LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS OR SERVICES; LOSS OF USE,
+// DATA, OR PROFITS; OR BUSINESS INTERRUPTION) HOWEVER CAUSED AND ON ANY
+// THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT LIABILITY, OR TORT
+// (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY OUT OF THE USE
+// OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF SUCH DAMAGE.
diff --git a/linux-aarch64/gn/METADATA b/linux-aarch64/gn/METADATA
new file mode 100644
index 0000000..3d94ed7
--- /dev/null
+++ b/linux-aarch64/gn/METADATA
@@ -0,0 +1,12 @@
+name: "GN"
+description: "GN is a meta-build system that generates NinjaBuild files."
+
+third_party {
+  url {
+    type: GIT
+    value: "https://gn.googlesource.com/gn"
+  }
+  version: "1901"
+  last_upgrade_date { year: 2021 month: 12 day: 16 }
+  license_type: NOTICE
+}
diff --git a/linux-aarch64/gn/README.md b/linux-aarch64/gn/README.md
index 2ff5702..b62d5ab 100644
--- a/linux-aarch64/gn/README.md
+++ b/linux-aarch64/gn/README.md
@@ -1,4 +1,4 @@
-gn 1452 (387e3ab4)
+gn 1901 (0d00acae)
 
 ``` shell
 git clone https://gn.googlesource.com/gn