added Intel GPU support for training and inference

[Jing1Ling]

Added 'xpu' device type, which represent Intel GPU.

Using Intel GPU for training and inference requires configuring oneAPI and IPEX. oneAPI: https://www.intel.com/content/www/us/en/developer/tools/oneapi/base-toolkit-download.html?operatingsystem=linux&distributions=offline IPEX: https://github.com/intel/intel-extension-for-pytorch

Example commands for running nerfstudio on XPU device:

# train
ns-train nerfacto --data data/nerfstudio/poster --machine.device-type xpu
# eval
ns-eval  --load-config=outputs/poster/nerfacto/exp_folder/config.yml
# render
ns-render dataset --load-config outputs/poster/nerfacto/exp_folder/config.yml