MFprojects/camlock r254895:
Add unmapped BIO support to GEOM ZERO if kern.geom.zero.clear is cleared.
Reimplement the FDOPT_NOERROR feature that was kicked out in r134081.

It is needed for fdread(1) in order to be able to recover from CRC
errors in the data field of a floppy sector (by returning the sector
data that failed CRC, rather than inventing dummy data).

When closing the device, clear all transient device options.

MFC after:	1 week