Move DAS routing setup into the DAS driver itself. This removes the need
to duplicate this in each machine driver, of which we'll soon have three.

An added advantage is that the machine drivers no longer call the Tegra20-
specific DAS functions by name, so the machine driver no longer needs to
be split up into Tegra20 and Tegra30 versions.

If individual machine drivers need a different routing setup to this
default, they can still call the DAS functions to set that up.

Long-term, DAS will be a codec driver, and user-space will be able to
control its routing, possibly within constraints that the machine driver
sets up. Configuring the DAS routing from the DAS driver is a very slight
move in that direction.
Signed-off-by: Stephen Warren <swarren@nvidia.com>
Signed-off-by: Mark Brown <broonie@opensource.wolfsonmicro.com>