ide: set WCACHE supported in IDENTIFY data

ide: set WCACHE supported in IDENTIFY data

ATA does not only have the WCACHE enabled bit in identify word 85, but also
a WCACHE supported bit in word 82.  While the Linux kernel is fine with the
latter at least hdparm also needs the former before correctly displaying
the cache settings.  There's also a non-zero chance other operating systems
are more picky in their volatile write cache detection.

Signed-off-by: Christoph Hellwig <hch@lst.de>
Signed-off-by: Kevin Wolf <kwolf@redhat.com>