mtd: spi-nor: Add support for w25q256jwm

Add support for Winbond 256M-bit flash w25q256jwm.
Performed basic erase/write/readback operations on
ZynqMP zc1751+dc1 board.

Signed-off-by: Venkatesh Yadav Abbarapu <venkatesh.abbarapu@amd.com>
Reviewed-by: Jagan Teki <jagan@amarulasolutions.com>