was being initialized to a KVA, when we really wanted a DMA address. Change
the code to allocate the overrun buffer with the control blocks, and
properly initialize overrun_buf.
Note that overrun_buf cannot actually be shared between all boards; DMA safe
memory could vary from bus to bus.
Garbage-collect two functions which are no longer used because of the
above changes.
struct scsipi_adapter; they were not used.
Add a scsipi_ioctl entry point to struct scsipi_adapter. This will be
used to issue ioctl commands to the host adapters.
Inspired by PR #6090, from Matt Jacob.
