V4L/DVB (3200): Fix saa7134 ALSA/OSS collisions

- When ALSA or OSS are loaded, check if the other is present
Fixed hotplug notifiers cleanup on module removal
- The saa7134 DMA sound modules now have their own Kconfig entries, and
if built statically enforce exclusivity
- SND_PCM_OSS isn't necessary for the OSS driver

Signed-off-by: Ricardo Cerqueira <v4l@cerqueira.org>
Signed-off-by: Mauro Carvalho Chehab <mchehab@brturbo.com.br>