standardize the code structure of the build.sh file

**Description:**

The `build.sh` file needs to be organized to follow the pattern of the other files

**How is the code:**

![image](https://user-images.githubusercontent.com/43859386/223567447-05f14ce3-834a-4e2b-a2ac-d1670c3f4e5d.png)

**What is expected:**

Following the kw code structure pattern we should start with a function like `kernel_build_main()`
