ALSA: hda - 4930g add internal lfe slider

Lately I sent patch that switched lfe with side in mixer for
acer-aspire-4930g. Then I connected 5.1 speaker system and noticed that
lfe slider wasn't working and that old lfe slider worked. What I'm doing
now is:

- reverting old patch
- adding internal lfe slider
- removing side as it is superfluous (ALC888S-VC is 7.1 but in fact
  laptop can only do 5.1 and it is so in drivers for MS Windows)

Signed-off-by: Łukasz Wojniłowicz <lukasz.wojnilowicz@gmail.com>
Signed-off-by: Takashi Iwai <tiwai@suse.de>