vmbase: Add basic logger

Introduce a logger in vmbase that wraps around the println! into UART to
be able to distinguish different levels of log messages.

Test: atest vmbase_example.integration_test
Change-Id: Id3b98ef4cdc4b23a11f099d75cc1c9902a9da785
diff --git a/vmbase/src/lib.rs b/vmbase/src/lib.rs
index 90d6fc2..257f415 100644
--- a/vmbase/src/lib.rs
+++ b/vmbase/src/lib.rs
@@ -18,6 +18,7 @@
 
 pub mod console;
 mod entry;
+pub mod logger;
 pub mod power;
 pub mod uart;