Add basic SPI support and associated documentation. v2: remove baud rate check, fix baud rate calculations v3: finish transaction with BSY check, disable SPI when not in use Signed-off-by: Grigori Goronzy <greg@chown.ath.cx>
Signed-off-by: Kevin O'Connor <kevin@koconnor.net>
Fixes #412. Signed-off-by: Grigori Goronzy <greg@chown.ath.cx>