wcaxx, wcte13xp, wcte43x: Honor max_latency module parameter.

The wcxb library did not do actually use the max_latency member to limit the
maximum latency of the DMA engine.

Now it does.

Signed-off-by: Shaun Ruffell <sruffell@digium.com>
Signed-off-by: Russ Meyerriecks <rmeyerriecks@digium.com>
wcte13xp: Export max_latency module parameter.

wcte13xp now has a max_latency module parameter like the wcaxx and wcte43x
drivers.

Signed-off-by: Shaun Ruffell <sruffell@digium.com>
Signed-off-by: Russ Meyerriecks <rmeyerriecks@digium.com>
wcte43x, wcte13xp: Use MSI interrupts if possible.

It was an oversight to prevent the wcte43x and wcte13xp drivers from using
Message Signaled interrupts during the switch to the wcxb library.

Signed-off-by: Shaun Ruffell <sruffell@digium.com>
Signed-off-by: Russ Meyerriecks <rmeyerriecks@digium.com>