FusionG3 operators. (#7315)

* Allow backends/cadence to use TestUtil.h. (#7304)

Summary:

Create a separate buck target for `TestUtil.h` that can be used by backends. The current `test_util` target has dependencies that don't compile for xtensa toolchain.

Reviewed By: zonglinpeng

Differential Revision: D67128600

* Xtensa ISS PAL layer for logging/timing. (#7311)

Summary:

Overrides for `et_pal*` weak symbols for logging/timing with xtensa ISS.

Reviewed By: zonglinpeng

Differential Revision: D67128599

* Use macro `XT_KERNEL_CHECK` to handle errors returned by nnlib. (#7312)

Summary:

Use ET_KERNEL_CHECK to detect error codes returned by xa_nn* library calls.

Reviewed By: zonglinpeng

Differential Revision: D67128597

* Separate buck targets per operator. (#7314)

Summary:

Keep targets separate so we only compile the operators we need.

Reviewed By: zonglinpeng

Differential Revision: D67128598

* FusionG3 operators. (#7315)

Summary:

Cleanup header order and `using` declarations for operators to match style guide.

Reviewed By: zonglinpeng

Differential Revision: D67128499