Put call to qstr_init and mp_init_emergency_exc_buf in mp_init.

qstr_init is always called exactly before mp_init, so makes sense to
just have mp_init call it.  Similarly with
mp_init_emergency_exception_buf.  Doing this makes the ports simpler and
less error prone (ie they can no longer forget to call these).
diff --git a/py/runtime.c b/py/runtime.c
index a478bb6..59e47c7 100644
--- a/py/runtime.c
+++ b/py/runtime.c
@@ -70,8 +70,13 @@
 };
 
 void mp_init(void) {
+    qstr_init();
     mp_stack_ctrl_init();
 
+#if MICROPY_ENABLE_EMERGENCY_EXCEPTION_BUF
+    mp_init_emergency_exception_buf();
+#endif
+
     // call port specific initialization if any
 #ifdef MICROPY_PORT_INIT_FUNC
     MICROPY_PORT_INIT_FUNC;