mtd: spi-nor: otp: implement erase for Winbond and similar flashes

mtd: spi-nor: otp: implement erase for Winbond and similar flashes

Winbond flashes with OTP support provide a command to erase the OTP
data. This might come in handy during development.

This was tested with a Winbond W25Q32JW on a LS1028A SoC with the
NXP FSPI controller.

Signed-off-by: Michael Walle <michael@walle.cc>
Signed-off-by: Vignesh Raghavendra <vigneshr@ti.com>
Reviewed-by: Pratyush Yadav <p.yadav@ti.com>
Reviewed-by: Tudor Ambarus <tudor.ambarus@microchip.com>