Move some of the definitions in LegacyNNDefinitions.cpp closer to sites (#37531)
Summary:
Pull Request resolved: https://github.com/pytorch/pytorch/pull/37531
All of these definitions are no longer "legacy" as their CPU
implementations have been ported to ATen. There are probably some
layers of indirection that could be reduced here, but for now just do a
minor but unlikely to break things cleanup.
The last thing in LegacyNNDefinitions truly is still in THCUNN and can't
be removed.
Signed-off-by: Edward Z. Yang <ezyang@fb.com>
Test Plan: Imported from OSS
Differential Revision: D21310913
Pulled By: ezyang
fbshipit-source-id: 1ff4ff16abddf13f8d583df990242ac4b0461915
