Adds support for Winbond's W25Q64 SPI flash. These devices are used on (among others) Xilinx' SP601 and SP605 Spartan-6 evaluation boards. Tested with "sf" commands. Signed-off-by: Graeme Smecher <graeme.smecher@mail.mcgill.ca> Signed-off-by: Mike Frysinger <vapier@gentoo.org>