ggml : move AMX to the CPU backend (#10570)

* ggml : move AMX to the CPU backend

---------

Co-authored-by: Georgi Gerganov <ggerganov@gmail.com>

ggml/src/ggml-cpu/llamafile/sgemm.cpp

@@ -50,8 +50,7 @@
 
 #include "sgemm.h"
 #include "ggml-impl.h"
-// hack until moved into the CPU backend
-#include "../ggml-cpu-impl.h"
+#include "ggml-cpu-impl.h"
 #include "ggml-quants.h"
 
 #ifdef _MSC_VER