mtd: spi-nor: Add support for w25q256jw

Add MTD support for w25q256jw SPI NOR chip from Winbond. This chip
supports dual/quad I/O mode with 512 blocks of memory organized in
64KB sectors. In addition to this, there is also small 4KB sectors
available for flexibility. The device has been validated using Thor96
board.

Cc: Marek Vasut <marek.vasut@gmail.com>
Cc: Tudor Ambarus <tudor.ambarus@microchip.com>
Cc: David Woodhouse <dwmw2@infradead.org>
Cc: Brian Norris <computersforpeace@gmail.com>
Cc: Miquel Raynal <miquel.raynal@bootlin.com>
Cc: Richard Weinberger <richard@nod.at>
Cc: Vignesh Raghavendra <vigneshr@ti.com>
Cc: linux-mtd@lists.infradead.org
Signed-off-by: Darshak Patel <darshak.patel@einfochips.com>
[Mani: cleaned up for upstream]
Signed-off-by: Manivannan Sadhasivam <manivannan.sadhasivam@linaro.org>
Signed-off-by: Tudor Ambarus <tudor.ambarus@microchip.com>