ALSA: hda - Rename power_mgmt flag with power_save_node

David suggested that the name "power_mgmt" is too ambiguous.  Rename
the flag with a bit clearer one "power_save_node".

Also, add the corresponding description to HD-Audio.txt, too.

Reported-by: David Henningsson <david.henningsson@canonical.com>
Signed-off-by: Takashi Iwai <tiwai@suse.de>

diff --cc Documentation/sound/alsa/HD-Audio.txt
Simple merge

diff --cc sound/pci/hda/hda_codec.h
Simple merge

diff --cc sound/pci/hda/hda_generic.c
Simple merge

diff --cc sound/pci/hda/patch_sigmatel.c
Simple merge

diff --cc sound/pci/hda/patch_via.c
Simple merge