GD32F103CB

[NIIBE Yutaka]

Hello,

In ShenZhen, I managed to get GD32F103CB.  It's LQFP48 version.  I
changed Chopstx so that it can work with GD32F103CB.  The changes are
clock setting for GD32F103 running 96MHz, and minor update of drivers
(USB driver, ADC driver, and flash protection).

Apparently, the peripherals are different implementations.

And the small change of drivers revealed a USB bug of NeuG/Gnuk, and
initialization problem of Fraucheky.  All fixed.
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