mtd: spi-nor: Remove support for Xilinx S3AN flashes

These flashes are kind of an oddball for the very old Xilinx Spartan 3
FPGAs to store their bitstream. More importantly, they reuse the Atmel
JEDEC manufacturer ID and in fact the at45db081d already blocks the use
of the 3S700AN flash chip. It's time to sunset support for these
flashes.

Signed-off-by: Michael Walle <mwalle@kernel.org>
Acked-by: Tudor Ambarus <tudor.ambarus@linaro.org>
Reviewed-by: Pratyush Yadav <pratyush@kernel.org>
Cc: Ricardo Ribalda <ribalda@kernel.org>
Acked-by: Ricardo Ribalda <ribalda@chromium.org>
Signed-off-by: Pratyush Yadav <pratyush@kernel.org>
Link: https://lore.kernel.org/r/20240419141249.609534-2-mwalle@kernel.org