* "remove cudnndevicecontext"

* "remove unused init code"

* "fix hash functions"

* "fix typo"

* "fix based on comments"

* "follow gogle style"

* "fix based on comemnts"

* fix bug in SetAttrDescVisitor

* add comments

* "fix data transform"

* "data transformer"

* "add device pool"

* "add test"

* "fix ci"

* "fix datalayout implementation "

* "fix based on comment"

* add helper function to get appropriate DeviceContext

* Run interface return future

* delete unused comments

* implement selectedrows serialize and deserialize

* make serialize/deserialize as global function

* recover send_imp.cc

* delete unused brackets

* fix compile error

* serialize version in LodTensor and SelecetedRows

* fix ci

* fix ci

* Rename API of DeviceContext

Make them as usual names.

* Rename API of DeviceContext

Make them as usual names.

* Fix compile

* Fix compile

* Fix compile

* Fix compile

* Fix compile

* "fix data transform"

* "split into next PR"

* fix bugs

* add KernelTypeToString interface

* cache memory in local scope

* fix typo

* refine trans logic

* "refine kernel registrar"

* "refine registrar with multikey"

* "fix register"

* "refine multikernel register"

* "fix CI"

* "fix CI"

* "fix registry"

* "swtich GPU to CUDA"

* "add register macro test case"

* "fix CI"

Make them as usual names.

Make them as usual names.

Make them as usual names.

* add memory switch mechanism in operator kernel switch

* init data_transform

* complete DataTransform

* fix build error

* add data_transform_test

* add a register test for data_transform_fn

* use function to simulate registration macro

* add register macro

* update test

* clean code

* restore unrelated code

* update data transform test

* generate unique name for REGISTER_DATA_TRANSFORM_FN

* add const

* follow comment

* update KernelTypePair hash function