esp32/modesp: Add osdebug() function to disable or change IDF logging.

Code lineage:
osdebug() is based loosely on the version in esp8266, but there didn't
seem to be an obvious way of choosing a particular UART. The basic
behavior is the same, though: provide None, and logging is disabled;
provide an integer and logging is restored to the default level.

To build on that, and because the IDF provides more functionality, a
second parameter has now been implemented which allows the active log
level to be set:

   esp.osdebug(uart[, level])

The module has a corresponding set of LOG_ values to set this accordingly.

ports/esp32/modesp.c

@@ -30,6 +30,7 @@
 #include <stdio.h>
 
 #include "rom/gpio.h"
+#include "esp_log.h"
 #include "esp_spi_flash.h"
 
 #include "py/runtime.h"
@@ -38,6 +39,23 @@
 #include "drivers/dht/dht.h"
 #include "modesp.h"
 
+STATIC mp_obj_t esp_osdebug(size_t n_args, const mp_obj_t *args) {
+    esp_log_level_t level = LOG_LOCAL_LEVEL;
+    if (n_args == 2) {
+        level = mp_obj_get_int(args[1]);
+    }
+    if (args[0] == mp_const_none) {
+        // Disable logging
+        esp_log_level_set("*", ESP_LOG_ERROR);
+    } else {
+        // Enable logging at the given level
+        // TODO args[0] should set the UART to which debug is sent
+        esp_log_level_set("*", level);
+    }
+    return mp_const_none;
+}
+STATIC MP_DEFINE_CONST_FUN_OBJ_VAR_BETWEEN(esp_osdebug_obj, 1, 2, esp_osdebug);
+
 STATIC mp_obj_t esp_flash_read(mp_obj_t offset_in, mp_obj_t buf_in) {
     mp_int_t offset = mp_obj_get_int(offset_in);
     mp_buffer_info_t bufinfo;
@@ -107,6 +125,8 @@ STATIC MP_DEFINE_CONST_FUN_OBJ_3(esp_neopixel_write_obj, esp_neopixel_write_);
 STATIC const mp_rom_map_elem_t esp_module_globals_table[] = {
     { MP_ROM_QSTR(MP_QSTR___name__), MP_ROM_QSTR(MP_QSTR_esp) },
 
+    { MP_ROM_QSTR(MP_QSTR_osdebug), MP_ROM_PTR(&esp_osdebug_obj) },
+
     { MP_ROM_QSTR(MP_QSTR_flash_read), MP_ROM_PTR(&esp_flash_read_obj) },
     { MP_ROM_QSTR(MP_QSTR_flash_write), MP_ROM_PTR(&esp_flash_write_obj) },
     { MP_ROM_QSTR(MP_QSTR_flash_erase), MP_ROM_PTR(&esp_flash_erase_obj) },
@@ -118,6 +138,14 @@ STATIC const mp_rom_map_elem_t esp_module_globals_table[] = {
 
     { MP_ROM_QSTR(MP_QSTR_neopixel_write), MP_ROM_PTR(&esp_neopixel_write_obj) },
     { MP_ROM_QSTR(MP_QSTR_dht_readinto), MP_ROM_PTR(&dht_readinto_obj) },
+
+    // Constants for second arg of osdebug()
+    { MP_ROM_QSTR(MP_QSTR_LOG_NONE), MP_ROM_INT((mp_uint_t)ESP_LOG_NONE)},
+    { MP_ROM_QSTR(MP_QSTR_LOG_ERROR), MP_ROM_INT((mp_uint_t)ESP_LOG_ERROR)},
+    { MP_ROM_QSTR(MP_QSTR_LOG_WARNING), MP_ROM_INT((mp_uint_t)ESP_LOG_WARN)},
+    { MP_ROM_QSTR(MP_QSTR_LOG_INFO), MP_ROM_INT((mp_uint_t)ESP_LOG_INFO)},
+    { MP_ROM_QSTR(MP_QSTR_LOG_DEBUG), MP_ROM_INT((mp_uint_t)ESP_LOG_DEBUG)},
+    { MP_ROM_QSTR(MP_QSTR_LOG_VERBOSE), MP_ROM_INT((mp_uint_t)ESP_LOG_VERBOSE)},
 };
 
 STATIC MP_DEFINE_CONST_DICT(esp_module_globals, esp_module_globals_table);