AP_HAL_SITL: convert to using hal.serial() instead of hal.uartX

libraries/AP_HAL_SITL/HAL_SITL_Class.cpp

@@ -182,7 +182,7 @@ void HAL_SITL::run(int argc, char * const argv[], Callbacks* callbacks) const
     _sitl_state->init(argc, argv);
 
     scheduler->init();
-    uartA->begin(115200);
+    serial(0)->begin(115200);
 
     rcin->init();
     rcout->init();
@@ -193,7 +193,7 @@ void HAL_SITL::run(int argc, char * const argv[], Callbacks* callbacks) const
     if (getenv("SITL_WATCHDOG_RESET")) {
         INTERNAL_ERROR(AP_InternalError::error_t::watchdog_reset);
         if (watchdog_load((uint32_t *)&utilInstance.persistent_data, (sizeof(utilInstance.persistent_data)+3)/4)) {
-            uartA->printf("Loaded watchdog data");
+            serial(0)->printf("Loaded watchdog data");
             utilInstance.last_persistent_data = utilInstance.persistent_data;
         }
     }

libraries/AP_HAL_SITL/SITL_State.cpp

@@ -216,7 +216,7 @@ void SITL_State::wait_clock(uint64_t wait_time_usec)
     // conditions.
     if (sitl_model->get_speedup() > 1) {
         while (true) {
-            const int queue_length = ((HALSITL::UARTDriver*)hal.uartA)->get_system_outqueue_length();
+            const int queue_length = ((HALSITL::UARTDriver*)hal.serial(0))->get_system_outqueue_length();
             // ::fprintf(stderr, "queue_length=%d\n", (signed)queue_length);
             if (queue_length < 1024) {
                 break;

libraries/AP_HAL_SITL/Scheduler.cpp

@@ -167,7 +167,7 @@ void Scheduler::system_initialized() {
 
 void Scheduler::sitl_end_atomic() {
     if (_nested_atomic_ctr == 0) {
-        hal.uartA->printf("NESTED ATOMIC ERROR\n");
+        hal.serial(0)->printf("NESTED ATOMIC ERROR\n");
     } else {
         _nested_atomic_ctr--;
     }
@@ -235,15 +235,9 @@ void Scheduler::_run_io_procs()
 
     _in_io_proc = false;
 
-    hal.uartA->_timer_tick();
-    hal.uartB->_timer_tick();
-    hal.uartC->_timer_tick();
-    hal.uartD->_timer_tick();
-    hal.uartE->_timer_tick();
-    hal.uartF->_timer_tick();
-    hal.uartG->_timer_tick();
-    hal.uartH->_timer_tick();
-    hal.uartI->_timer_tick();
+    for (uint8_t i=0; i<hal.num_serial; i++) {
+        hal.serial(i)->_timer_tick();
+    }
     hal.storage->_timer_tick();
 
 #ifndef HAL_BUILD_AP_PERIPH