MFC r260581:

 - Add sglist_append_bio(9) to append a struct bio's data to a sglist
MFC r260581:

 - Add sglist_append_bio(9) to append a struct bio's data to a sglist
MFC r260582, r260583:

 - Add unmapped IO support to virtio_blk(4)
 - Add unmapped IO support to virtio_scsi(4)
MFC r261147, r261149:

 - Remove spaces before tabs in the function prototype list
 - Read each field of the configuration individually