Support CPU input for device QuantileDMatrix. (#8136)

- Copy `GHistIndexMatrix` to `Ellpack` when needed.

src/common/hist_util.cuh

@@ -17,6 +17,28 @@
 
 namespace xgboost {
 namespace common {
+namespace cuda {
+/**
+ * copy and paste of the host version, we can't make it a __host__ __device__ function as
+ * the fn might be a host only or device only callable object, which is not allowed by nvcc.
+ */
+template <typename Fn>
+auto __device__ DispatchBinType(BinTypeSize type, Fn&& fn) {
+  switch (type) {
+    case kUint8BinsTypeSize: {
+      return fn(uint8_t{});
+    }
+    case kUint16BinsTypeSize: {
+      return fn(uint16_t{});
+    }
+    case kUint32BinsTypeSize: {
+      return fn(uint32_t{});
+    }
+  }
+  SPAN_CHECK(false);
+  return fn(uint32_t{});
+}
+}  // namespace cuda
 
 namespace detail {
 struct EntryCompareOp {