ALSA: hda/realtek - Make input path parser more generic

Now we reached to the final big piece of parser rewrite: the input
paths.  While the old parser code assumes the more-or-less direct and
similar connections from input pin to ADC, the new code handles the
complete input paths.  The capture source is switched by simple calls
of activate_path() function.

The parsing of capture volume and capture switches is, however, not
fully generalized.  It assumes that amps are available in the vicinity
of ADCs (in three depth).  This isn't perfect but it should cover all
codecs I know of.

Also, this commit removes some NID mapping of capture-related controls
temporarily for simplicity.  It'll be restored in later commits.

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