Basic Vulkan Multi-GPU implementation (ggml-org#5321)

* Initial Vulkan multi-gpu implementation

Move most global variables into backend context

* Add names to backend device functions

* Add further missing cleanup code

* Reduce code duplication in tensor split layer assignment

* generalize LLAMA_SPLIT_LAYER for all backends, do not expose device count and memory in llama.h

* Only do device info print in the beginning and initialize one backend for cpu assist

Add missing cleanup code

* Rework backend memory management to make sure devices and buffers get properly allocated and freed

* Rename cpu assist free function

---------

Co-authored-by: slaren <slarengh@gmail.com>

common/common.cpp

@@ -46,6 +46,10 @@
 #define GGML_USE_CUBLAS_SYCL
 #endif
 
+#if (defined(GGML_USE_CUBLAS) || defined(GGML_USE_SYCL)) || defined(GGML_USE_VULKAN)
+#define GGML_USE_CUBLAS_SYCL_VULKAN
+#endif
+
 int32_t get_num_physical_cores() {
 #ifdef __linux__
     // enumerate the set of thread siblings, num entries is num cores
@@ -660,8 +664,8 @@ bool gpt_params_parse_ex(int argc, char ** argv, gpt_params & params) {
                     params.tensor_split[i] = 0.0f;
                 }
             }
-#ifndef GGML_USE_CUBLAS_SYCL
-            fprintf(stderr, "warning: llama.cpp was compiled without cuBLAS/SYCL. Setting a tensor split has no effect.\n");
+#ifndef GGML_USE_CUBLAS_SYCL_VULKAN
+            fprintf(stderr, "warning: llama.cpp was compiled without cuBLAS/SYCL/Vulkan. Setting a tensor split has no effect.\n");
 #endif // GGML_USE_CUBLAS_SYCL
         } else if (arg == "--no-mmap") {
             params.use_mmap = false;