Add a minimum rsa key size config to psa config

Signed-off-by: Waleed Elmelegy <waleed.elmelegy@arm.com>
diff --git a/include/mbedtls/rsa.h b/include/mbedtls/rsa.h
index 3d57aa2..8045e6b 100644
--- a/include/mbedtls/rsa.h
+++ b/include/mbedtls/rsa.h
@@ -85,6 +85,10 @@
 // Regular implementation
 //
 
+#if !defined(MBEDTLS_RSA_MIN_KEY_SIZE)
+#define MBEDTLS_RSA_MIN_KEY_SIZE 1024
+#endif
+
 /**
  * \brief   The RSA context structure.
  */