CHROMIUM: ASoC: tegra: Implement SPDIF CPU DAI

CHROMIUM: ASoC: tegra: Implement SPDIF CPU DAI

This is a minimal driver for the Tegra SPDIF controller.

In hardware, the SPDIF signal is always routed to any active HDMI display
controllers, and may also be routed to external pins on Tegra. This
minimal driver is targetted purely at HDMI usage, but may work for the
SPDIF pins too, given the correct pinmux settings.

Signed-off-by: Stephen Warren <swarren@nvidia.com>;

BUG=
TEST=

[Stephen Warren, 2011-03-04 21:27:35]

This series of patches implements audio-over-HDMI support:

http://codereview.chromium.org/6625021
http://codereview.chromium.org/6623022
http://codereview.chromium.org/6626025
http://codereview.chromium.org/6632011
http://codereview.chromium.org/6624031
http://codereview.chromium.org/6624032
http://codereview.chromium.org/6623023
http://codereview.chromium.org/6625022

The series requires two other series to be merged first:
* My series to backport upstream ASoC into ChromeOS
  (strictly necessary in all likelihood)
* Robert's series to rework the dc driver
  (perhaps not required; some small amount of merging may be required
  in order to merge this first though)

[Olof Johansson, 2011-03-07 03:41:32]

I'll apply this, but two nitpicks that should be considered when you upstream:

1) new drivers are normally preferred to keep without defaults (i.e. default n).
ARM isn't quite as picky as x86 on this though.

2) the TEGRA_SPDIF_* defines are loong. Since they're driver-local in scope and
name space pollution isn't quite an issue, I would consider abbreviating them a
bit to make the lines shorter.