implementation of SpiDevice for auto NSS (chip select)

[lgjonathan]

Right now, the spi in the HAL only implements SpiBus, which leaves the CS(NSS) management to user software. If the SpiDevice trait from embedded_hal is implemented, then the user don't have to care about the NSS management since it will be taken care by the hardware.

I'm relatively new to the embedded world and I was wondering if such implementation will be too complicated to pull off. If not, I'm willing to try implement it myself. Would HardwareCS from the stm32h7 be a good reference to begin with?

Thanks