This reverts commit 0c25ad80.

The original commit disabled the aamixer path due to the noise
problem, but it turned out that some mobo with the same PCI SSID
doesn't suffer from the issue, and the disabled function (analog
loopback) is still demanded by users.

Since the recent commit [e7fdd527: ALSA: hda - Implement loopback
control switch for Realtek and other codecs], we have the dynamic
mixer switch to enable/disable the aamix path, and we don't have to
disable the path statically any longer.  So, let's revert the
disablement, so that only the user suffering from the noise problem
can turn off the aamix on the fly.

Bugzilla: https://bugzilla.kernel.org/show_bug.cgi?id=108301
Reported-by: <mutedbytes@gmail.com>
Cc: <stable@vger.kernel.org>
Signed-off-by: Takashi Iwai <tiwai@suse.de>