Add MBEDTLS_LMS_PRIVATE define

To enable private key operations

Signed-off-by: Raef Coles <raef.coles@arm.com>
diff --git a/library/lmots.h b/library/lmots.h
index ca7d4bf..e784bf5 100644
--- a/library/lmots.h
+++ b/library/lmots.h
@@ -101,6 +101,7 @@
                                                      Boolean values only. */
 } mbedtls_lmots_public_t;
 
+#ifdef MBEDTLS_LMS_PRIVATE
 /** LMOTS private context structure.
  *
  * A LMOTS private key is one hash output for each of digit of the digest +
@@ -124,6 +125,7 @@
     unsigned char MBEDTLS_PRIVATE(have_private_key); /*!< Whether the context contains a private key.
                                                      Boolean values only. */
 } mbedtls_lmots_private_t;
+#endif /* MBEDTLS_LMS_PRIVATE */
 
 /**
  * \brief                    This function converts an unsigned int into a
@@ -256,6 +258,8 @@
                           size_t msg_size, const unsigned char *sig,
                           size_t sig_size );
 
+#ifdef MBEDTLS_LMS_PRIVATE
+
 /**
  * \brief                    This function initializes a private LMOTS context
  *
@@ -375,6 +379,7 @@
                         void *p_rng, const unsigned char *msg, size_t msg_size,
                         unsigned char *sig, size_t sig_size, size_t* sig_len );
 
+#endif /* MBEDTLS_LMS_PRIVATE */
 
 #ifdef __cplusplus
 }