[PyTorch Mobile] Mark xnnpack operators selective
Summary: The remaining operator registrations that are not marked as selective. The size save is -12.2 KB for igios and -14 KB for fbios.
Test Plan: CI
Reviewed By: dhruvbird
Differential Revision: D25742543
fbshipit-source-id: 3e58789d36d216a52340c00b53e2f783ea2c9414
