sf: winbond: Add W25Q64W

Add support for Winbond's W25Q64W SPI flash.
This device is used on xilinx zynq emulation platform.

Signed-off-by: Jagannadha Sutradharudu Teki <jaganna@xilinx.com>
Signed-off-by: Michal Simek <michal.simek@xilinx.com>