MFC r301296,r301297,r301300:

r301296 (by cem):

ioat(4): Make channel indices unsigned

r301297 (by cem):

ioat(4): Export the number of available channels

r301300 (by cem):

ioat(4): Always log capabilities on attach

Different, relatively recent Intel Xeon hardware support radically different
features. E.g., BDX support CRC32 while BDX-DE does not.