nvk: Upload shaders on the CPU when we have ReBAR

Without without resizable BAR, we're limited as to how much VRAM we can
map and we sometimes run out of maps for games with large numbers of
shaders.  We keep using the DMA engine fallback in that case.

Part-of: <https://gitlab.freedesktop.org/mesa/mesa/-/merge_requests/26622>

src/nouveau/vulkan/nvk_device.c

@@ -191,12 +191,18 @@ nvk_CreateDevice(VkPhysicalDevice physicalDevice,
    if (result != VK_SUCCESS)
       goto fail_images;
 
-   /* The I-cache pre-fetches and we don't really know by how much.  Over-
-    * allocate shader BOs by 4K to ensure we don't run past.
+   /* If we have a full BAR, go ahead and do shader uploads on the CPU.
+    * Otherwise, we fall back to doing shader uploads via the upload queue.
+    *
+    * Also, the I-cache pre-fetches and we don't really know by how much.
+    * Over-allocating shader BOs by 4K ensures we don't run past.
     */
+   enum nouveau_ws_bo_map_flags shader_map_flags = 0;
+   if (pdev->info.bar_size_B >= pdev->info.vram_size_B)
+      shader_map_flags = NOUVEAU_WS_BO_WR;
    result = nvk_heap_init(dev, &dev->shader_heap,
                           NOUVEAU_WS_BO_LOCAL | NOUVEAU_WS_BO_NO_SHARE,
-                          0 /* map_flags */,
+                          shader_map_flags,
                           4096 /* overalloc */,
                           dev->pdev->info.cls_eng3d < VOLTA_A);
    if (result != VK_SUCCESS)