Cleanup license metadata in external/rust/crates/gbm.

Add package and license module in Android.bp. File LICENSE is from upstream project, so use it in Android.bp.

Bug: 346390141
Change-Id: Ic0dc5d52ec708ea0b91c7d49ff5fd075d35c51a2
Test: CIs
diff --git a/Android.bp b/Android.bp
index d614f40..7787824 100644
--- a/Android.bp
+++ b/Android.bp
@@ -1,9 +1,17 @@
 // This file is generated by cargo_embargo.
-// Do not modify this file after the first "rust_*" or "genrule" module
-// because the changes will be overridden on upgrade.
-// Content before the first "rust_*" or "genrule" module is preserved.
+// Do not modify this file because the changes will be overridden on upgrade.
 
-// TODO: Add license.
+package {
+    default_applicable_licenses: ["external_rust_crates_gbm_license"],
+}
+
+license {
+    name: "external_rust_crates_gbm_license",
+    visibility: [":__subpackages__"],
+    license_kinds: ["SPDX-license-identifier-MIT"],
+    license_text: ["LICENSE"],
+}
+
 rust_library {
     name: "libgbm_rust",
     host_supported: true,
diff --git a/cargo_embargo.json b/cargo_embargo.json
index f275bc5..6744c1e 100644
--- a/cargo_embargo.json
+++ b/cargo_embargo.json
@@ -1,4 +1,9 @@
 {
+  "package": {
+    "gbm": {
+      "license_text": "LICENSE"
+    }
+  },
   "run_cargo": false,
   "module_name_overrides": {
     "libdrm": "libdrm_rust",