Add warning to mbedtls_ecp_set_max_ops()

Using PSA interruptible interfaces will cause previously set values to be
overwritten.

Signed-off-by: Paul Elliott <paul.elliott@arm.com>
diff --git a/include/mbedtls/ecp.h b/include/mbedtls/ecp.h
index 7a28a19..1590ef2 100644
--- a/include/mbedtls/ecp.h
+++ b/include/mbedtls/ecp.h
@@ -472,6 +472,12 @@
  *                  only enabled for specific sides and key exchanges
  *                  (currently only for clients and ECDHE-ECDSA).
  *
+ * \warning         Using the PSA interruptible interfaces with keys in local
+ *                  storage and no accelerator driver will also call this
+ *                  function to set the values specified via those interfaces,
+ *                  overwriting values previously set. Care should be taken if
+ *                  mixing these two interfaces.
+ *
  * \param max_ops   Maximum number of basic operations done in a row.
  *                  Default: 0 (unlimited).
  *                  Lower (non-zero) values mean ECC functions will block for