Use an enum to specify the various quirks instead of #defines inside the
structure definition.

[mkp: fix typo]

Link: https://lore.kernel.org/r/20200221140812.476338-3-hch@lst.deReviewed-by: Bart Van Assche <bvanassche@acm.org>
Signed-off-by: Christoph Hellwig <hch@lst.de>
Signed-off-by: Martin K. Petersen <martin.petersen@oracle.com>