avmd:Make libavmd no_std

Bug: 240459942
Test: m avmdtool
Change-Id: I395ddd7aba970c5ff94b8eff7b8d06a553ff036d
diff --git a/avmd/src/avmd.rs b/avmd/src/avmd.rs
index e3bc7a7..50cdfdf 100644
--- a/avmd/src/avmd.rs
+++ b/avmd/src/avmd.rs
@@ -12,9 +12,15 @@
 // See the License for the specific language governing permissions and
 // limitations under the License.
 
+extern crate alloc;
+
+use alloc::{
+    string::{String, ToString},
+    vec::Vec,
+};
 use apexutil::to_hex_string;
+use core::fmt;
 use serde::{Deserialize, Serialize};
-use std::fmt;
 
 /// An Avmd struct contains
 /// - A header with version information that allows rollback when needed.
diff --git a/avmd/src/lib.rs b/avmd/src/lib.rs
index 9722518..7a06e6a 100644
--- a/avmd/src/lib.rs
+++ b/avmd/src/lib.rs
@@ -14,6 +14,8 @@
 
 //! Library for handling AVMD blobs.
 
+#![no_std]
+
 mod avmd;
 
 pub use avmd::{ApkDescriptor, Avmd, Descriptor, ResourceIdentifier, VbMetaDescriptor};