add rknn runtime for rockchips

[enthropy7]

Why do we need this?

RKNN is an inference framework for the NPU on Rockchip devices (RK3588, RK356x, etc.). RKNN stands for Rockchip Neural Network.

A user must first convert a model to the .rknn format using the RKNN Toolkit, and then run it on their device through the RKNN Runtime, which uses the NPU for execution.

So, this is essentially NPU support for Rockchip devices.