Add Chacha dependency to the stream cipher field
When MBEDTLS_ARC4_C and MBEDTLS_CIPHER_NULL_CIPHER were disabled, the stream
cipher function wasn't being include in the cipher struct, yet Chacha20 requires
it.
#define MBEDTLS_CIPHER_MODE_WITH_PADDING
#endif
-#if defined(MBEDTLS_ARC4_C) || defined(MBEDTLS_CIPHER_NULL_CIPHER)
+#if defined(MBEDTLS_ARC4_C) || defined(MBEDTLS_CIPHER_NULL_CIPHER) || \
+ defined(MBEDTLS_CHACHA20_C)
#define MBEDTLS_CIPHER_MODE_STREAM
#endif
