V4L/DVB (8311): sms1xxx: support device-specific firmware filenames on stellar usb1 sticks

Add the capability to define device-specific firmware filenames for the SMS1010,
with a mechanism to fall back to the generic firmware if the device-specific
firmware is not present.

Signed-off-by: Michael Krufky <mkrufky@linuxtv.org>
Signed-off-by: Mauro Carvalho Chehab <mchehab@infradead.org>