metal : map the CPU buffers to Metal buffers (WIP)

ggml-metal.h

@@ -34,9 +34,17 @@
 extern "C" {
 #endif
 
-// GG: maybe return ptr and avoid the "ggml.h" include
 struct ggml_backend * ggml_backend_metal_init(struct ggml_backend * backend_cpu);
 
+// TODO: temporary - move to backend interface
+bool ggml_backend_metal_map_buffer(
+        struct ggml_backend * backend,
+                 const char * name,
+                       void * data,
+                     size_t   size,
+                     size_t   max_size);
+
+
 //struct ggml_metal_context;
 //
 //// number of command buffers to use