Reduce build size of op_pixel_shuffle & op_pixel_unshuffle (#6020)

Summary:
Pull Request resolved: https://github.com/pytorch/executorch/pull/6020

pixel_shuffle:     60 K -> 1.8 K
pixel_unshuffle: 57 K -> 1.7 K
ghstack-source-id: 246985128
exported-using-ghexport

Reviewed By: malfet, swolchok

Differential Revision: D63994872

fbshipit-source-id: 1840abf154c71ec18f66ed47e38dfe1caa317ddd