spi-nor: Add Winbond w25m512jv

Similar to the other ones, different size. The "JV" suffix is in
the datasheet, I haven't seen mentions of a different one.

The datasheet indicates DUAL and QUAD are supported.

 http://www.winbond.com/resource-files/w25m512jv%20revc%2001062017.pdf



Signed-off-by: Benjamin Herrenschmidt <benh@kernel.crashing.org>
Signed-off-by: Joel Stanley <joel@jms.id.au>
Signed-off-by: Cyrille Pitchen <cyrille.pitchen@wedev4u.fr>