API change for bus_dma

[Justin T. Gibbs]

>  > As I understand it, it is possible to set the pycho bridge to use
>  > a coherent address range, but FreeBSD doesn't take advantage of that
>  > yet.
>  > 
> 
> Yes, that's what solaris does..

We added BUS_DMA_COHERENT to the API just before shipping 5.1.  It
is only a "hint", so if you need to verify that the implementation
was able to give you coherent memory, we should add an API to allow
you to know.  Of course, the Sparc bus dma implementation doesn't honor
the flag yet, but I'm sure that will change shortly.

--
Justin