Bootloader NVS decryption uses hardware ROM APIs to decrypt the NVS contents,
but for targets that do not support AES hardware we could benefit by using the
software mbedtls library that is present in the ROM directly.
add: private include header
add: macro encapsulation for assertion or error check
add: ESP_FAIL return code documentation in public headers
change: replaced all assertions by NVS_ASSERT_OR_RETURN macro
change: few internal function return values from void to esp_err_t
change: ESP_ERR_NVS_VALUE_TOO_LONG macro comment
