ALSA: HDA: Conexant auto: Handle multiple connections to ADC node

Conexant 20641 has several inputs to its ADC node, with one selector
and individual amps for all inputs. This patch adds support in the
Conexant auto parser to handle that case.

It also means that the pin node's volume is being renamed to "Boost"
to avoid name clash with the new volume controls on the ADC node.

BugLink: http://bugs.launchpad.net/bugs/719524


Signed-off-by: David Henningsson <david.henningsson@canonical.com>
Signed-off-by: Takashi Iwai <tiwai@suse.de>