E3C/E4C SSDs do support the Write Zeroes command in theory, but have very
bad performance when using it.  As the firmware has been frozen for these
products we can not expect firmware improvements for it, so disable
Write Zeroes.
Signed-off-by: Tina Hsu <tina_hsu@phison.corp-partner.google.com>
[hch: update the commit message]
Signed-off-by: Christoph Hellwig <hch@lst.de>