ggml: Export GPU UUIDs

This enables matching up devices and information reported by the backend
with system management libraries such as nvml to get accurate free
memory reporting.

ml/backend/ggml/ggml/include/ggml-backend.h

@@ -152,6 +152,7 @@ extern "C" {
     struct ggml_backend_dev_props {
         const char * name;
         const char * description;
+        const char * uuid;
         size_t memory_free;
         size_t memory_total;
         enum ggml_backend_dev_type type;