Add log for memory init

Author: Azure-stars

os/src/main.rs

@@ -103,6 +103,7 @@ pub fn rust_main() -> ! {
     clear_bss();
     kernel_log_info();
     mm::init();
+    println!("after mm::init!");
     mm::remap_test();
     task::add_initproc();
     println!("after initproc!");