[ALSA] hda: ALC260 test model implementation

[ALSA] hda: ALC260 test model implementation

Modules: HDA Codec driver

The following patch adds a 'test' ALC260 model specification to the
patch_realtek.c driver if CONFIG_SND_DEBUG is set.  This is similar to the
'test' ALC880 model in that it sets up mixer controls for almost everything
to make it easier for people to test their laptop/soundcard when working out
what pin widgets are connected to which real-world devices.

This patch assumes my previous patch (adding the second PCM to the ALC260)
has previously been applied since it uses infrastructure added by that
patch.

In developing this patch it was found that not all retasking pins accept all
the modes - in particular, some ignore the VREFxx variants.  The pin mode
control has therefore been tweaked to prevent this becoming a problem in
mixer applications.

Signed-off-by: Takashi Iwai <tiwai@suse.de>