V4L/DVB (3293): Added digital support for cx88 (cx88-alsa)

V4L/DVB (3293): Added digital support for cx88 (cx88-alsa)

- This module is co-authored by  Ricardo Cerqueira <v4l@cerqueira.org>.

- Added digital audio support for cx88-based boards that have function
  01 enabled. These boards can be identified by having PCI id 1471:8801
  or 1471:8811.

- Increased DMA buffer from 512 to 4096 seems to fix audio distortion.

- Existing audio DMA uses conflict with cx88-alsa. Should be disabled when
  cx88-alsa module is compiled.

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