mpl/cuda: Only initialize hooks from free functions

Instead of initializing all GPU infrastructure, just setup hooks. This
still avoids crashes and won't cause consume resources if the user is
simply allocating and freeing device memory not for use with MPI.

src/mpl/src/gpu/mpl_gpu_cuda.c

@@ -508,9 +508,8 @@ __attribute__ ((visibility("default")))
 CUresult CUDAAPI cuMemFree(CUdeviceptr dptr)
 {
     CUresult result;
-    if (!gpu_initialized) {
-        int ret = MPL_gpu_init(0);
-        assert(ret == 0);
+    if (!sys_cuMemFree) {
+        gpu_mem_hook_init();
     }
 
     gpu_free_hooks_cb((void *) dptr);
@@ -524,9 +523,8 @@ __attribute__ ((visibility("default")))
 cudaError_t CUDARTAPI cudaFree(void *dptr)
 {
     cudaError_t result;
-    if (!gpu_initialized) {
-        int ret = MPL_gpu_init(0);
-        assert(ret == 0);
+    if (!sys_cudaFree) {
+        gpu_mem_hook_init();
     }
 
     gpu_free_hooks_cb(dptr);