mtd: spi-nor: Add support for Winbond w25q64dw serial flash

Add Winbond (w25q64dw) 8MB flash to the list of supported chips.

Signed-off-by: Mika Westerberg <mika.westerberg@linux.intel.com>
Signed-off-by: Brian Norris <computersforpeace@gmail.com>