ALSA: scarlett2: Add support for uploading new firmware

Add ops.write to the hwdep interface. Once the upgrade firmware flash
segment has been erased, writes to the hwdep fd are permitted, and
translated to SCARLETT2_USB_WRITE_SEGMENT commands to the device.

Signed-off-by: Geoffrey D. Bennett <g@b4.vu>
Link: https://lore.kernel.org/r/ZY65S0ojShSNSeRQ@m.b4.vu


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