flashchips: Add AT25SF321

This commit adds support for the Adesto AT25SF321 SPI flash chip. Probe
and read operations have been tested via FT2232H interface, but writes
have not been verified.

Datasheet is available at the following URL:
https://www.adestotech.com/wp-content/uploads/DS-AT25SF321_047.pdf



Change-Id: I7410815e063ffe154a97d7ea5881c8eb82025f56
Signed-off-by: Peter Adkins <pete@kernelpicnic.net>
Reviewed-on: https://review.coreboot.org/c/flashrom/+/36904


Tested-by: build bot (Jenkins) <no-reply@coreboot.org>
Reviewed-by: David Hendricks <david.hendricks@gmail.com>