XCHAN_CAP_BOUNCE.
The only application that uses bounce buffering for now is the Government
Furnished Equipment (GFE) P2's dma core (AXIDMA) with its own dedicated
cacheless bounce buffer.
Sponsored by: DARPA, AFRL
As cs is stored in a uint32_t, use the last bit to store the
active high flag as it's unlikely that we will have that much CS.
Reviewed by: loos
MFC after: 2 weeks
Differential Revision: https://reviews.freebsd.org/D8614