stmhal: Use MICROPY_EVENT_POLL_HOOK instead of __WFI where appropriate.

stmhal/mphalport.c

@@ -43,7 +43,7 @@ int mp_hal_stdin_rx_chr(void) {
         } else if (MP_STATE_PORT(pyb_stdio_uart) != NULL && uart_rx_any(MP_STATE_PORT(pyb_stdio_uart))) {
             return uart_rx_char(MP_STATE_PORT(pyb_stdio_uart));
         }
-        __WFI();
+        MICROPY_EVENT_POLL_HOOK
     }
 }
 

stmhal/uart.c

@@ -334,7 +334,7 @@ STATIC bool uart_rx_wait(pyb_uart_obj_t *self, uint32_t timeout) {
         if (HAL_GetTick() - start >= timeout) {
             return false; // timeout
         }
-        __WFI();
+        MICROPY_EVENT_POLL_HOOK
     }
 }
 
@@ -375,7 +375,7 @@ STATIC bool uart_tx_wait(pyb_uart_obj_t *self, uint32_t timeout) {
         if (HAL_GetTick() - start >= timeout) {
             return false; // timeout
         }
-        __WFI();
+        MICROPY_EVENT_POLL_HOOK
     }
 }