[mlir][spirv] Implement gpu::TargetAttrInterface (#69949)

This commit implements gpu::TargetAttrInterface for SPIR-V target
attribute. The plan is to use this to enable GPU compilation pipeline
for OpenCL kernels later.

The changes do not impact Vulkan shaders using milr-vulkan-runner.
New GPU Dialect transform pass spirv-attach-target is implemented for
attaching attribute from CLI.

gpu-module-to-binary pass now works with GPU module that has SPIR-V
module with OpenCL kernel functions inside.