Instead of using the HAL functions we can just use the defines from the
board support for the longan nano that comes with the nuclei-sdk. Also
we move some includes and defines to the header file.
The core of tinyusb must be as independent as possible, we previously
relied on nuclei-sdk or the GD32VF103 firmware library for the synopsys
driver to work with the GD32VF103. Fortunatly we needed very few parts
from them so we implement them here.
Without having __riscv_flen defined we get multiple warinings. But
defining it causes the startup code to contain floating point instructions.
This results in a exception right after booting.
See startup_gd32vf103.S lines 289-294 should open a PR at nuclei sdk
Stefan Kerkmann