io is currently handeled by io_duart only.

a generic io buffer is implemented in basic/iobuf.h basic/iobuf.c

up 'till now, both ports of the DUART have drivers. Channel B 
is the console port. Its iobuf is called krnlin and krnlout and is only
available inside io_duart. Channel A uses struct iobuf rdioin and rdioout
and two support functions rdioput and rdioget. 


