After extensive QA cycles at 3ware, bring the driver in-line with all the
issues which they found and asked to be changed so 3ware can offcially
support the driver.

Summary of the most significant changes:

• TWE_OVERRIDE is no longer supported
• If twe_getparam failed, bogus data would be returned to the caller
• Cache the device unit in the twe_drive structure to aid debugging
• Add the 3ware driver version.
• Proper return error codes for many functions.
• Track the minimum queue length statistics
• 4.x compat: use the cached unit number from the twe_drive structure instead of the the cached si_drv2. 3ware found that after many loads and unloads that si_drv2 became corrupted. This did not happen in -current.

Submitted by: Vinod Kashyap (with modifications by me)
Approved by: re (rwatson)