Copy stable/9 to releng/9.3 as part of the 9.3-RELEASE cycle.

Approved by: re (implicit)
Sponsored by: The FreeBSD Foundation

Copy head to stable/9 as part of 9.0-RELEASE release cycle.

Approved by: re (implicit)

Clean up some magic numbers in the DBDMA code by replacing them with
appropriately defined constants.

Suggested by: gnn

Change the DBDMA API to allow DBDMA registers in a subregion of a resource. This is necessary to allow future support of DMA for the various Apple on-board ATA controllers.

MFC after: 1 week

Add support for Apple's Descriptor-Based DMA (DBDMA) engine. The DMA
engine is usful to various existing drivers, such as ata(4) and scc(4),
and is used bhy the soon to be added bm(4).

Submitted by: Nathan Whitehorn