[iOS GPU][Stub] Move conv2d_prepack impl from MetalPrepackOpRegister.cpp to MetalConvolution.cpp (#56491)
Summary:
Pull Request resolved: https://github.com/pytorch/pytorch/pull/56491
Move the prepack convolution to the op file to get rid of the selective compilation.
ghstack-source-id: 126960054
Test Plan: CI
Reviewed By: SS-JIA
Differential Revision: D27719539
fbshipit-source-id: 75fb3849858a31a915828a0f5f6f3d4066ff4c9b
