ALSA: usb-audio: scarlett2: Split struct scarlett2_ports

The scarlett2_ports struct contains both generic (hardware IDs and
descriptions) and model-specific (port count) data. Remove the generic
data from the scarlett2_device_info struct so it is not repeated for
every model.
Signed-off-by: Geoffrey D. Bennett <g@b4.vu>
Link: https://lore.kernel.org/r/7a9e57e4e55a482390c692a9e60731d72b664a15.1624294591.git.g@b4.vuSigned-off-by: Takashi Iwai <tiwai@suse.de>