pytorch: enable gpu for apple mps

[mqy]

This commit roughly enables mps for the d2l's pytorch implementation.
Tested on mac 13.2.1 (intel chip), with pytorch 1.12 and 1.13.

You may want to have a look at the references here:

• https://pytorch.org/docs/stable/notes/mps.html
• https://developer.apple.com/metal/pytorch/

How to test on MacOS:

import sys
sys.path.append('/path/to/local/d2l-en/pytorch/')
from d2l import torch as d2l
d2l.num_gpus()

1

[d2l-bot]

Job d2l-en/PR-2453/1 is complete.
Check the results at http://preview.d2l.ai/d2l-en/PR-2453/

[d2l-bot]

Job d2l-en/PR-2453/2 is complete.
Check the results at http://preview.d2l.ai/d2l-en/PR-2453/