subsys: console: tty: Allow to specify receive timeout

This allows to specify receive timeout, instead of previously
hardcoded K_FOREVER value. K_FOREVER is still the default, and can
be changes after tty initialization using tty_set_rx_timeout() call,
and timeout is stored as a property of tty. (Instead of e.g. being
a param of each receive call. Handling like that is required for
POSIX-like behavior of tty).

Signed-off-by: Paul Sokolovsky <paul.sokolovsky@linaro.org>