esp8266: Support dedicated REPL loop (aka pull-style).

Event-driven loop (push-style) is still supported and default (controlled
by MICROPY_REPL_EVENT_DRIVEN setting, as expected).

Dedicated loop worked even without adding ets_loop_iter(), though that
needs to be revisited later.

esp8266/esp_mphal.c

@@ -66,7 +66,7 @@ void mp_hal_delay_us(uint32_t us) {
 
 int mp_hal_stdin_rx_chr(void) {
     for (;;) {
-        int c = uart0_rx();
+        int c = ringbuf_get(&input_buf);
         if (c != -1) {
             return c;
         }
@@ -156,7 +156,9 @@ void __assert_func(const char *file, int line, const char *func, const char *exp
 }
 
 void mp_hal_signal_input(void) {
+    #if MICROPY_REPL_EVENT_DRIVEN
     system_os_post(UART_TASK_ID, 0, 0);
+    #endif
 }
 
 static int call_dupterm_read(void) {

esp8266/main.c

@@ -62,15 +62,38 @@ void soft_reset(void) {
     mp_hal_stdout_tx_str("PYB: soft reboot\r\n");
     mp_hal_delay_us(10000); // allow UART to flush output
     mp_reset();
+    #if MICROPY_REPL_EVENT_DRIVEN
     pyexec_event_repl_init();
+    #endif
 }
 
 void init_done(void) {
+    #if MICROPY_REPL_EVENT_DRIVEN
     uart_task_init();
+    #endif
     mp_reset();
     mp_hal_stdout_tx_str("\r\n");
+    #if MICROPY_REPL_EVENT_DRIVEN
     pyexec_event_repl_init();
+    #endif
     dupterm_task_init();
+
+    #if !MICROPY_REPL_EVENT_DRIVEN
+soft_reset:
+    for (;;) {
+        if (pyexec_mode_kind == PYEXEC_MODE_RAW_REPL) {
+            if (pyexec_raw_repl() != 0) {
+                break;
+            }
+        } else {
+            if (pyexec_friendly_repl() != 0) {
+                break;
+            }
+        }
+    }
+    soft_reset();
+    goto soft_reset;
+    #endif
 }
 
 void user_init(void) {

esp8266/uart.c

@@ -233,6 +233,7 @@ void soft_reset(void);
 void mp_keyboard_interrupt(void);
 
 int interrupt_char;
+#if MICROPY_REPL_EVENT_DRIVEN
 void uart_task_handler(os_event_t *evt) {
     if (pyexec_repl_active) {
         // TODO: Just returning here isn't exactly right.
@@ -264,3 +265,4 @@ void uart_task_handler(os_event_t *evt) {
 void uart_task_init() {
     system_os_task(uart_task_handler, UART_TASK_ID, uart_evt_queue, sizeof(uart_evt_queue) / sizeof(*uart_evt_queue));
 }
+#endif