ALSA: hda - Add CS4208 codec support for MacBook 6,1 and 6,2

MacBook 6,1 and 6,2 have a CS4208 codec instead of CS4206/CS4207 on
the former models.  Most of functions work fine as is, except for the
silent speaker output.  After debugging sessions, it turned out that
the machine needs to set GPIO 0 for the speaker amp.

This patch adds the basic support for CS4208 and the fixup for these
MacBooks.  Basically the codec works just with the generic parser.
For re-using the existing GPIO amp code and init/free callbacks, a few
places have been changed so that CS4206/4207-specific codes (errata,
etc) won't hit with CS4208.

Bugzilla: https://bugzilla.kernel.org/show_bug.cgi?id=60811
Reported-and-tested-by: Imre Kaloz <kaloz@openwrt.org>
Reported-and-tested-by: Ian Munsie <darkstarsword@gmail.com>
Signed-off-by: Takashi Iwai <tiwai@suse.de>