New macro PSA_KEY_EXPORT_MAX_SIZE

Sufficient buffer size for psa_export_key() and psa_export_public_key().
diff --git a/include/psa/crypto.h b/include/psa/crypto.h
index 837f737..87f2d60 100644
--- a/include/psa/crypto.h
+++ b/include/psa/crypto.h
@@ -1243,6 +1243,12 @@
  * \retval #PSA_ERROR_EMPTY_SLOT
  * \retval #PSA_ERROR_NOT_PERMITTED
  * \retval #PSA_ERROR_NOT_SUPPORTED
+ * \retval #PSA_ERROR_BUFFER_TOO_SMALL
+ *         The size of the \p data buffer is too small. You can determine a
+ *         sufficient buffer size by calling
+ *         #PSA_KEY_EXPORT_MAX_SIZE(\c type, \c bits)
+ *         where \c type is the key type
+ *         and \c bits is the key size in bits.
  * \retval #PSA_ERROR_COMMUNICATION_FAILURE
  * \retval #PSA_ERROR_HARDWARE_FAILURE
  * \retval #PSA_ERROR_TAMPERING_DETECTED
@@ -1332,6 +1338,14 @@
  * \retval #PSA_SUCCESS
  * \retval #PSA_ERROR_EMPTY_SLOT
  * \retval #PSA_ERROR_INVALID_ARGUMENT
+ *         The key is neither a public key nor a key pair.
+ * \retval #PSA_ERROR_NOT_SUPPORTED
+ * \retval #PSA_ERROR_BUFFER_TOO_SMALL
+ *         The size of the \p data buffer is too small. You can determine a
+ *         sufficient buffer size by calling
+ *         #PSA_KEY_EXPORT_MAX_SIZE(#PSA_KEY_TYPE_PUBLIC_KEY_OF_KEYPAIR(\c type), \c bits)
+ *         where \c type is the key type
+ *         and \c bits is the key size in bits.
  * \retval #PSA_ERROR_COMMUNICATION_FAILURE
  * \retval #PSA_ERROR_HARDWARE_FAILURE
  * \retval #PSA_ERROR_TAMPERING_DETECTED