ALSA: scarlett2: Add skeleton hwdep/ioctl interface

Add skeleton hwdep/ioctl interface, beginning with
SCARLETT2_IOCTL_PVERSION and SCARLETT2_IOCTL_REBOOT.

Signed-off-by: Geoffrey D. Bennett <g@b4.vu>
Link: https://lore.kernel.org/r/24ffcd47a8a02ebad3c8b2438104af8f0169164e.1703001053.git.g@b4.vu


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