* feat(): dynamic_to_static support for ipu.

* fix(): format fix.

* fix format

* fix cpplint error

* use phi::errors

* fix format

* fix format

* fix(): add api to restore patched function.

* fix(): identity_loss uses cpu place as expected kernel type.

* doc(): add IPU dy2static related docs.

* fix(): combine test cases.

* fix format

* fix comment

* fix format

* apply comment

* fix compiling

* fix(): align docs.

* fix(): fix identity_loss function docs.

* fix(): adjust mean and sum in identity_loss.

* fix(): minor docs.

* move API to paddle.incubate.identity_loss

* fix UT
Co-authored-by: Nzhaorui chen <zhaoruic@graphcore.ai>