[ALSA] HDA/ALC260: 3/7 - generalise some structures

Modules: HDA Codec driver

This patch generalises a structure added for the 'fujitsu' model but which
is potentially useful for other models as well.  It turns the
'alc260_fujitsu_adc_nids' array into 'alc260_dual_adc_nids'; for other
models which decide to utilise the dual ADC functionality there's really
no reason why they need to define their own list of ADC nids.

The 'fujitsu' model preset is adjusted accordingly.

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