ALSA: jack - Add "Line In" input jack constants

Similar to Line Out, these constants form the base for future
patches enabling input jack reporting for Line in jacks.

Signed-off-by: David Henningsson <david.henningsson@canonical.com>
Acked-by: Mark Brown <broonie@opensource.wolfsonmicro.com>
Signed-off-by: Takashi Iwai <tiwai@suse.de>