ggml-zendnn : add ZenDNN backend for AMD CPUs (#17690)

* ggml-zennn: add ZenDNN backend support

* ggml-zendnn : address ZenDNN backend review fixes and suggestions

* docs : apply blockquote syntax to ZenDNN docs

---------

Co-authored-by: Manoj Kumar <mkumar@zettabolt.com>

ggml/include/ggml-zendnn.h

@@ -0,0 +1,22 @@
+#pragma once
+
+#include "ggml-backend.h"
+#include "ggml.h"
+
+#ifdef __cplusplus
+extern "C" {
+#endif
+
+// backend API
+GGML_BACKEND_API ggml_backend_t ggml_backend_zendnn_init(void);
+
+GGML_BACKEND_API bool ggml_backend_is_zendnn(ggml_backend_t backend);
+
+// number of threads used for zendnn operations
+GGML_BACKEND_API void ggml_backend_zendnn_set_n_threads(ggml_backend_t backend_zendnn, int n_threads);
+
+GGML_BACKEND_API ggml_backend_reg_t ggml_backend_zendnn_reg(void);
+
+#ifdef __cplusplus
+}
+#endif