esp32/network_lan: Support configuration of ETH ref_clk pin.

Both the direction and the Pin used for ref_clk can now be configured.  It
Requires at least idf v4.4.  The new keyword arguments to the constructor
are:

- ref_clk_mode=mode: with mode being Pin.IN or Pin.OUT.  If it is not set,
  then the default configuration is used, which may be configured by
  kconfig settings.

- ref_clk=pin_obj: which defines the Pin used for ref_clk.  This is either
  Pin(0), Pin(16) or Pin(17).  No check is done for the pin number.  If it
  is the wrong one, it simply will not work.  Besides that, no harm.

ports/esp32/network_lan.c

@@ -97,7 +97,8 @@ STATIC mp_obj_t get_lan(size_t n_args, const mp_obj_t *pos_args, mp_map_t *kw_ar
         return MP_OBJ_FROM_PTR(&lan_obj);
     }
 
-    enum { ARG_id, ARG_mdc, ARG_mdio, ARG_power, ARG_phy_addr, ARG_phy_type };
+    enum { ARG_id, ARG_mdc, ARG_mdio, ARG_power, ARG_phy_addr, ARG_phy_type,
+           ARG_ref_clk_mode, ARG_ref_clk };
     static const mp_arg_t allowed_args[] = {
         { MP_QSTR_id,           MP_ARG_OBJ, {.u_obj = mp_const_none} },
         { MP_QSTR_mdc,          MP_ARG_KW_ONLY | MP_ARG_REQUIRED | MP_ARG_OBJ },
@@ -105,6 +106,11 @@ STATIC mp_obj_t get_lan(size_t n_args, const mp_obj_t *pos_args, mp_map_t *kw_ar
         { MP_QSTR_power,        MP_ARG_KW_ONLY | MP_ARG_OBJ, {.u_obj = mp_const_none} },
         { MP_QSTR_phy_addr,     MP_ARG_KW_ONLY | MP_ARG_REQUIRED | MP_ARG_INT },
         { MP_QSTR_phy_type,     MP_ARG_KW_ONLY | MP_ARG_REQUIRED | MP_ARG_INT },
+        // Dynamic ref_clk configuration available at v4.4
+        #if ESP_IDF_VERSION_MINOR >= 4
+        { MP_QSTR_ref_clk_mode, MP_ARG_KW_ONLY | MP_ARG_INT, {.u_int = -1} },
+        { MP_QSTR_ref_clk,      MP_ARG_KW_ONLY | MP_ARG_OBJ, {.u_obj = mp_const_none} },
+        #endif
     };
 
     mp_arg_val_t args[MP_ARRAY_SIZE(allowed_args)];
@@ -139,6 +145,17 @@ STATIC mp_obj_t get_lan(size_t n_args, const mp_obj_t *pos_args, mp_map_t *kw_ar
     eth_mac_config_t mac_config = ETH_MAC_DEFAULT_CONFIG();
     mac_config.smi_mdc_gpio_num = self->mdc_pin;
     mac_config.smi_mdio_gpio_num = self->mdio_pin;
+    // Dynamic ref_clk configuration available at v4.4
+    #if ESP_IDF_VERSION_MINOR >= 4
+    if (args[ARG_ref_clk_mode].u_int != -1) {
+        // Map the GPIO_MODE constants to EMAC_CLK constants.
+        mac_config.clock_config.rmii.clock_mode =
+            args[ARG_ref_clk_mode].u_int == GPIO_MODE_INPUT ? EMAC_CLK_EXT_IN : EMAC_CLK_OUT;
+    }
+    if (args[ARG_ref_clk].u_obj != mp_const_none) {
+        mac_config.clock_config.rmii.clock_gpio = machine_pin_get_id(args[ARG_ref_clk].u_obj);
+    }
+    #endif
     esp_eth_mac_t *mac = esp_eth_mac_new_esp32(&mac_config);
 
     eth_phy_config_t phy_config = ETH_PHY_DEFAULT_CONFIG();