Since akg supports both Ascend and Gpu, but their supported type and format are different,
so we use two directory "ascend" and "gpu" to store their registers respectively, and use
an attribute "processor" to distinguish them.

Main changes:
1) Add two op register class "AkgAscendRegOp" and "AkgGpuRegOp", inherited from the original AkgRegOp.
2) Rewrite akg ascend op registers with new interface, move them into directory "ascend".
3) Rename the imply_type from "AutoDiff" to "AKG".
4) Modify function FindOp, check the processor when imply_type is "AKG".
5) Modify function CheckRepetition, remove the judgement for impl_path, check processor instead.

TODO: Remove op registers in akg root path.

- It provides a unified style to express graph and kernel for user.
- It provides a unified IR to represent graph and kernel for developer.
- It breaks the boundary between graph and kernel.
- It provides more opportunities to do compile optimization.

Signed-off-by: leonwanghui <leon.wanghui@huawei.com>