Move common gpu primitives to backend/gpu (#2145)

mlx/backend/gpu/copy.h

@@ -0,0 +1,46 @@
+// Copyright © 2023-2024 Apple Inc.
+
+#pragma once
+
+#include "mlx/backend/common/copy.h"
+#include "mlx/stream.h"
+
+#include <optional>
+
+namespace mlx::core {
+
+// Generic copy inplace
+void copy_gpu_inplace(
+    const array& in,
+    array& out,
+    const Shape& data_shape,
+    const Strides& i_strides,
+    const Strides& o_strides,
+    int64_t i_offset,
+    int64_t o_offset,
+    CopyType ctype,
+    const Stream& s,
+    const std::optional<array>& dynamic_i_offset = std::nullopt,
+    const std::optional<array>& dynamic_o_offset = std::nullopt);
+
+void copy_gpu(const array& src, array& out, CopyType ctype, const Stream& s);
+void copy_gpu(const array& src, array& out, CopyType ctype);
+
+void copy_gpu_inplace(
+    const array& in,
+    array& out,
+    CopyType ctype,
+    const Stream& s);
+
+void copy_gpu_inplace(
+    const array& in,
+    array& out,
+    const Strides& i_strides,
+    int64_t i_offset,
+    CopyType ctype,
+    const Stream& s);
+
+// Fill the output with the scalar val
+void fill_gpu(const array& val, array& out, const Stream& s);
+
+} // namespace mlx::core