nvs: add config to ignore "encrypted" flag of nvs partitions

This is to allow having pre IDF v4.3 behavior where "encrypted"
flag was not being checked for NVS partitions.

It is recommended to enable this new config only if you have
production devices where NVS partition was being set with "encrypted"
flag by mistake.

Please see commit aca9ec28b3d091a73605ee89ab63f8f76a996491 which
introduced check to not allow NVS partitions with "encrypted" flag set.

More discussion on this at:
https://github.com/espressif/esp-idf/issues/5747#issuecomment-956223024
https://github.com/espressif/esp-idf/issues/7839#issuecomment-961477667

Closes https://github.com/espressif/esp-idf/issues/7839
Closes IDFGH-6162

components/nvs_flash/Kconfig

@@ -9,4 +9,15 @@ menu "NVS"
             the complete NVS data, except the page headers. It requires XTS encryption keys
             to be stored in an encrypted partition. This means enabling flash encryption is
             a pre-requisite for this feature.
+
+    config NVS_COMPATIBLE_PRE_V4_3_ENCRYPTION_FLAG
+        bool "NVS partition encrypted flag compatible with ESP-IDF before v4.3"
+        depends on SECURE_FLASH_ENC_ENABLED
+        help
+            Enabling this will ignore "encrypted" flag for NVS partitions. NVS encryption
+            scheme is different than hardware flash encryption and hence it is not recommended
+            to have "encrypted" flag for NVS partitions. This was not being checked in pre v4.3
+            IDF. Hence, if you have any devices where this flag is kept enabled in partition
+            table then enabling this config will allow to have same behavior as pre v4.3 IDF.
+
 endmenu

components/spi_flash/partition.c

@@ -235,6 +235,15 @@ static esp_err_t load_partitions(void)
             item->info.encrypted = true;
         }
 
+#if CONFIG_NVS_COMPATIBLE_PRE_V4_3_ENCRYPTION_FLAG
+        if (entry.type == ESP_PARTITION_TYPE_DATA &&
+                    entry.subtype == ESP_PARTITION_SUBTYPE_DATA_NVS &&
+                    (entry.flags & PART_FLAG_ENCRYPTED)) {
+            ESP_LOGI(TAG, "Ignoring encrypted flag for \"%s\" partition", entry.label);
+            item->info.encrypted = false;
+        }
+#endif
+
         // item->info.label is initialized by calloc, so resulting string will be null terminated
         strncpy(item->info.label, (const char*) entry.label, sizeof(item->info.label) - 1);