pc_serial: Fix TTYSETRTS

Same fix as hrev42151 for usb_serial:
When determining the bit to be set for RTS/DTR there was a missing comparison
to op which would've caused a wrong line state to be set.
pc_serial: This one really is B31250
pc_serial: Use two tty cookies
pc_serial: Drop BeOS stuff

Even I don't use it anymore...