mtd: spi: Add Macronix MX66U2G45F device

Add Macronix MX66U2G45F flash device description.
This is a 256 MiB part.

Signed-off-by: Marek Vasut <marex@denx.de>
Cc: Simon Goldschmidt <simon.k.r.goldschmidt@gmail.com>
Cc: Vignesh R <vigneshr@ti.com>
[jagan: use 'g' instead of 'f' in flash name]
Signed-off-by: Jagan Teki <jagan@amarulasolutions.com>