Some pins are used for controlling the LED with the VREF value.
This patch changes the power behavior of such pins to be constantly
up.  A new state, pin_fixed, is introduced to nid_path to indicate
that the path contains the fixed pin.  This improves also the
readability a bit for other static routes, too.

Then a helper function snd_hda_gen_fix_pin_power() is called from the
codec driver for such fixed pins, and it will create fake paths
containing only these pins with pin_fixed=1 flag.
Reported-by: David Henningsson <david.henningsson@canonical.com>
Signed-off-by: Takashi Iwai <tiwai@suse.de>