[ALSA] HDA/ALC260: 4/7 - add GPIO switches to test model

Modules: HDA Codec driver

This patch adds 'test' model mixer switches for the GPIO controls found on
the ALC260.  It has been found that some laptops (eg: Acer) can use these to
enable particular controls, so it would be useful to have access to these
via the 'test' model.  It will make testing new models easy, especially if
certain outputs cannot be made to work any other way.

This patch *should* work, but because the GPIO pins don't do anything in
my laptop I cannot personally verify that all this works as expected.

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