Feat: kernel thread done

kernel/lib/thread.S

@@ -0,0 +1,21 @@
+.global context_switch
+context_switch:
+	stp x19, x20, [x0, 16 * 0]
+	stp x21, x22, [x0, 16 * 1]
+	stp x23, x24, [x0, 16 * 2]
+	stp x25, x26, [x0, 16 * 3]
+	stp x27, x28, [x0, 16 * 4]
+	stp fp, lr, [x0, 16 * 5]
+	mov x9, sp
+	str x9, [x0, 16 * 6]
+
+	ldp x19, x20, [x1, 16 * 0]
+	ldp x21, x22, [x1, 16 * 1]
+	ldp x23, x24, [x1, 16 * 2]
+	ldp x25, x26, [x1, 16 * 3]
+	ldp x27, x28, [x1, 16 * 4]
+	ldp fp, lr, [x1, 16 * 5]
+	ldr x9, [x1, 16 * 6]
+	mov sp,  x9
+	msr tpidr_el1, x2
+	ret