MFC r260509:
Replace several instances of -1 with appropriate CAM_*_WILDCARD and types.

It was equal before r259397, but for good or bad, not any more for LUNs.

This change fixes at least CAM debugging.
MFC r264406:
Report more readable state "-" for idle CAM scan thread.
MFC r264834:
Disable UNMAP support for STEC 842 SSDs.

In some unknown cases UNMAP commands make device firmware stuck.