Update documentation for set_flush_denormal support on ARM (#119354)
**Documentation update for set_flush_denormal():**
-> set_flush_denormal() is now supported on ARM CPU's.
-> **PR:** https://github.com/pytorch/pytorch/pull/115184 (Already merged)
**Reference page:** https://pytorch.org/docs/stable/generated/torch.set_flush_denormal.html
Pull Request resolved: https://github.com/pytorch/pytorch/pull/119354
Approved by: https://github.com/drisspg
