Let's have more orthogonal and cleaner API, where buffers are
configured by tty_set_rx_buf/tty_set_tx_buf, and only them. It
means that newly initialized tty starts in unbuffered mode, which
is somewhat a sidestep from a main usecase behind tty, which is
buffered operation, but again, having a cleaner API (and good
docs, explaining users how it should be and what they should do)
prevails.
Signed-off-by: Paul Sokolovsky <paul.sokolovsky@linaro.org>