esp32/machine_uart: Add support for LP_UART.

Signed-off-by: Andrew Leech <andrew@alelec.net>

ports/esp32/machine_uart.c

@@ -453,12 +453,18 @@ static mp_obj_t mp_machine_uart_make_new(const mp_obj_type_t *type, size_t n_arg
             self->rx = 9;
             self->tx = 10;
             break;
-        #if SOC_UART_NUM > 2
+        #if SOC_UART_HP_NUM > 2
         case UART_NUM_2:
             self->rx = 16;
             self->tx = 17;
             break;
         #endif
+        #if SOC_UART_LP_NUM >= 1
+        case LP_UART_NUM_0:
+            self->rx = 4;
+            self->tx = 5;
+        #endif
+
     }
 
     #if MICROPY_HW_ENABLE_UART_REPL