[iOS GPU][BE][5/n] Remove indirection calls from MPSCNNOps.mm and MetalAten.mm (#53432)
Summary:
Pull Request resolved: https://github.com/pytorch/pytorch/pull/53432
1. Creating individual .mm files for each op under the ops/ folder, and each op just has it's own function. The op is registered at the end of the file.
2. Remove the indirection calls from MetalAten.mm to MPSCNNOps.mm
3. Delete MPSCNNOps.mm
ghstack-source-id: 123205443
Test Plan:
1. Sandcastle
2. CircleCI
3. Mobilelab
Reviewed By: SS-JIA
Differential Revision: D26840953
fbshipit-source-id: e1664c8d7445fdbd3b016c4dd51de0a6294af3a5
