ALSA: scarlett2: Add ioctl commands to erase flash segments

Add ioctls:
- SCARLETT2_IOCTL_SELECT_FLASH_SEGMENT
- SCARLETT2_IOCTL_ERASE_FLASH_SEGMENT
- SCARLETT2_IOCTL_GET_ERASE_PROGRESS

The settings or the firmware flash segment can be selected and then
erased (asynchronous operation), and the erase progress can be
monitored.

If the erase progress is not monitored, then subsequent hwdep
operations will block until the erase is complete.

Once the erase is started, ALSA controls that communicate with the
device will all return -EBUSY, and the device must be rebooted.

Signed-off-by: Geoffrey D. Bennett <g@b4.vu>
Link: https://lore.kernel.org/r/227409adb672f174bf3db211e9bda016fb4646ea.1703001053.git.g@b4.vu


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