ggml : ggml_compute_forward_concat() for arbitrary tensor type (#1118)

ggml : ggml_compute_forward_concat() for arbitrary tensor type (#1118)

* ggml_compute_forward_concat() for arbitrary tensor type

* Check that tensors' type match

* ggml-cpu.c: check type of source tensors

* ggml-cpu.c: move tensor type check to ggml_compute_forward_concat()

* ggml.c: check concatenated tensor type

* Remove tensor type check from ggml_compute_forward_concat() in ggml-cpu.c

..., as it was moved to ggml.c.