cpu/esp*: nfs_flash/cpp dependency cleanup

Module `esp_idf_nvs_flash` uses C++ code. Since  `esp_idf_nvs_flash` module is always enabled on ESP8266, the permanent dependency on `cpp` is correct. But on ESP32, the `esp_idf_nvs_flash` module is only enabled if `esp_wifi_any` is used. Only in that case the compilation should depend on module `cpp`.

cpu/esp32/vendor/esp-idf/nvs_flash/Kconfig

@@ -9,6 +9,7 @@ config MODULE_ESP_IDF_NVS_FLASH
     bool
     depends on TEST_KCONFIG
     depends on MODULE_ESP_IDF
+    select MODULE_CPP
     select MODULE_MTD
     help
         Non-volatile storage library.

cpu/esp8266/vendor/esp-idf/nvs_flash/src/Kconfig

@@ -9,5 +9,6 @@ config MODULE_ESP_IDF_NVS_FLASH
     bool
     depends on TEST_KCONFIG
     depends on MODULE_ESP_IDF
+    select MODULE_CPP
     help
         Non-volatile storage library.

cpu/esp_common/Makefile.dep

@@ -25,7 +25,10 @@ USEMODULE += xtensa
 # Features used by ESP*
 
 FEATURES_REQUIRED += newlib
-FEATURES_REQUIRED += cpp # Vendor code uses C++
+
+ifneq (,$(filter esp_idf_nvs_flash,$(USEMODULE)))
+  FEATURES_REQUIRED += cpp
+endif
 
 ifneq (,$(filter esp_wifi_ap,$(USEMODULE)))
   FEATURES_REQUIRED += esp_wifi_ap

cpu/esp_common/esp_common.config

@@ -6,6 +6,3 @@ CONFIG_MODULE_PRNG_MUSL_LCG=y
 CONFIG_MODULE_PERIPH_HWRNG=y
 CONFIG_MODULE_PERIPH_UART=y
 CONFIG_MODULE_NEWLIB=y
-
-# Vendor code uses C++
-CONFIG_MODULE_CPP=y