Adds syscall for sleep and print and makes process work in user mode

src/user.rs

@@ -0,0 +1,19 @@
+use core::time::Duration;
+
+use crate::syscall::{sleep, write_string_temp};
+
+pub extern "C" fn test() {
+    loop {
+        write_string_temp("test");
+        // enable_supervisor_interrupt();
+        sleep(Duration::new(2, 0));
+    }
+}
+
+pub extern "C" fn proc2() {
+    loop {
+        write_string_temp("proc2");
+        // enable_supervisor_interrupt();
+        sleep(Duration::new(3, 0));
+    }
+}