[SCSI] wd33c93: Fast SCSI with WD33C93B

Attached are patches, which help to utilize more of the WD33C93B SCSI
controller's capabilities.

1) Added/changed all the necessary code to enable Burst Mode DMA. Only
   Single Byte DMA was used before.

2) Added/changed all the necessary code to enable Fast-10 SCSI transfers.

3) The original driver inadvertently used a transfer period of 1000-800ns
   (the lowest possible transfer rate) for asynchronous data transfers,
   instead of the (configurable) default period intended for this purpose,
   if the target responded to a SDTR not with a Reject-message, but with
   a zero-SDTR. This issue was fixed.
   Moreover, in case of a Reject the driver used the default-period's
   initialization-value instead of its (maybe smaller) current value. The
   missing assignment was added.

4) The driver's commandline- and proc-file-interface was augmented to
   handle the new options properly.

The WD33C93 manual, found at
http://www.datasheet.in/datasheet-html/W/D/3/WD33C93B_WesternDigital.pdf.html,
was very helpful.

Signed-off-by: peter fuerst <post@pfrst.de>
Signed-off-by: James Bottomley <James.Bottomley@SteelEye.com>