Try to create descriptor buffer buffer if failing to create wholeMemBuf

* On some drivers such as radv there are memory types only accessible via
  descriptor buffer usage flags, and it's important to have a wholeMemBuf to
  readback both for maps (quite possible/likely) as well as initial contents.

renderdoc/driver/vulkan/wrappers/vk_resource_funcs.cpp

@@ -715,11 +715,38 @@ VkResult WrappedVulkan::vkAllocateMemory(VkDevice device, const VkMemoryAllocate
       }
       else
       {
-        // can't create a memory-spanning buffer for this allocation. Assume this is a case where
-        // this memory type is only available to images and is not mappable - in which case the
-        // whole memory buffer won't be needed so we can skip this.
         ObjDisp(device)->DestroyBuffer(Unwrap(device), wholeMemBuf, NULL);
         wholeMemBuf = VK_NULL_HANDLE;
+
+        // can't create a memory-spanning buffer for this allocation. Try again with descriptor
+        // buffers if that is enabled as those memory types are sometimes unique.
+        if(DescriptorBuffers())
+        {
+          bufInfo.usage |= VK_BUFFER_USAGE_RESOURCE_DESCRIPTOR_BUFFER_BIT_EXT;
+
+          ret = ObjDisp(device)->CreateBuffer(Unwrap(device), &bufInfo, NULL, &wholeMemBuf);
+          RDCASSERTEQUAL(ret, VK_SUCCESS);
+
+          ObjDisp(device)->GetBufferMemoryRequirements(Unwrap(device), wholeMemBuf, &mrq);
+
+          RDCASSERTEQUAL(mrq.size, info.allocationSize);
+
+          if((mrq.memoryTypeBits & (1U << info.memoryTypeIndex)) != 0)
+          {
+            bufid = GetResourceManager()->WrapResource(Unwrap(device), wholeMemBuf);
+
+            ObjDisp(device)->BindBufferMemory(Unwrap(device), Unwrap(wholeMemBuf), Unwrap(*pMemory),
+                                              0);
+          }
+          else
+          {
+            ObjDisp(device)->DestroyBuffer(Unwrap(device), wholeMemBuf, NULL);
+            wholeMemBuf = VK_NULL_HANDLE;
+          }
+        }
+
+        // Otherwise this could be a case where this memory type is only available to images and is
+        // not mappable - in which case the whole memory buffer shouldn't be needed so we can skip this.
       }
     }