Debug: Add functions for ECDH contexts

The SSL module accesses ECDH context members directly to print debug
information. This can't work with the new context, where we can't make
assumptions about the implementation of the context. This commit adds
new debug functions to complete the encapsulation of the ECDH context
and work around the problem.
diff --git a/library/debug.c b/library/debug.c
index db3924a..824cd02 100644
--- a/library/debug.c
+++ b/library/debug.c
@@ -365,4 +365,54 @@
 }
 #endif /* MBEDTLS_X509_CRT_PARSE_C */
 
+#if defined(MBEDTLS_ECDH_C)
+static void mbedtls_debug_printf_ecdh_internal( const mbedtls_ssl_context *ssl,
+                                                int level, const char *file,
+                                                int line,
+                                                const mbedtls_ecdh_context *ecdh,
+                                                mbedtls_debug_ecdh_attr attr )
+{
+#if defined(MBEDTLS_ECDH_LEGACY_CONTEXT)
+    const mbedtls_ecdh_context* ctx = ecdh;
+#else
+    const mbedtls_ecdh_context_mbed* ctx = &ecdh->ctx.mbed_ecdh;
+#endif
+
+    switch( attr )
+    {
+        case MBEDTLS_DEBUG_ECDH_Q:
+            mbedtls_debug_print_ecp( ssl, level, file, line, "ECDH: Q",
+                                     &ctx->Q );
+            break;
+        case MBEDTLS_DEBUG_ECDH_QP:
+            mbedtls_debug_print_ecp( ssl, level, file, line, "ECDH: Qp",
+                                     &ctx->Qp );
+            break;
+        case MBEDTLS_DEBUG_ECDH_Z:
+            mbedtls_debug_print_mpi( ssl, level, file, line, "ECDH: z",
+                                     &ctx->z );
+            break;
+        default:
+            break;
+    }
+}
+
+void mbedtls_debug_printf_ecdh( const mbedtls_ssl_context *ssl, int level,
+                                const char *file, int line,
+                                const mbedtls_ecdh_context *ecdh,
+                                mbedtls_debug_ecdh_attr attr )
+{
+#if defined(MBEDTLS_ECDH_LEGACY_CONTEXT)
+    mbedtls_debug_printf_ecdh_internal( ssl, level, file, line, ecdh, attr );
+#else
+    switch( ecdh->var )
+    {
+        default:
+            mbedtls_debug_printf_ecdh_internal( ssl, level, file, line, ecdh,
+                                                attr );
+    }
+#endif
+}
+#endif /* MBEDTLS_ECDH_C */
+
 #endif /* MBEDTLS_DEBUG_C */