leds: ledtrig-tty: Make rx tx activitate configurable

Until now, the LED blinks when data is sent via the tty (rx/tx).
This is not configurable.

This change adds the possibility to make the indication for the direction
of the transmitted data independently controllable via the new rx and
tx sysfs entries.

- rx:
  Signal reception (rx) of data on the named tty device.
  If set to 0, the LED will not blink on reception.
  If set to 1 (default), the LED will blink on reception.

- tx:
  Signal transmission (tx) of data on the named tty device.
  If set to 0, the LED will not blink on transmission.
  If set to 1 (default), the LED will blink on transmission.

This new sysfs entry are on by default. Thus the trigger behaves as
before this change.

Signed-off-by: Florian Eckert <fe@dev.tdt.de>
Reviewed-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
Link: https://lore.kernel.org/r/20231127110311.3583957-4-fe@dev.tdt.de


Signed-off-by: Lee Jones <lee@kernel.org>