ALSA: scarlett2: Split scarlett2_config_items[] into 3 sections

ALSA: scarlett2: Split scarlett2_config_items[] into 3 sections

scarlett2_config_items[] contains the parameters for the configuration
items. The driver previously had two sets of configurations items; one
for devices with no mixer, and one for devices with a mixer. This
patch splits the latter into two (one set for Gen 2 devices and one
set for Gen 3 devices) in preparation for a new item (standalone)
which is present in both but with a different offset.

Signed-off-by: Geoffrey D. Bennett <g@b4.vu>
Link: https://lore.kernel.org/r/20969f9ea500684e978c87067fbdc7e73de1f6ed.1646578164.git.g@b4.vu
Signed-off-by: Takashi Iwai <tiwai@suse.de>