aarch64: Add a set_tcb method to setup tpidr_el0

src/context/arch/aarch64.rs

@@ -104,6 +104,10 @@ impl Context {
         self.lr = address;
     }
 
+    pub fn set_tcb(&mut self, pid: usize) {
+        self.tpidr_el0 = (crate::USER_TCB_OFFSET + pid * crate::PAGE_SIZE);
+    }
+
     pub fn set_fp(&mut self, address: usize) {
         self.fp = address;
     }