flashchips: Add Boya BY25D20/40

Only tested reading the BY25D40, using an FT232H.
Datasheet: https://www.lcsc.com/datasheet/C384591.pdf

Change-Id: Ibf2075de76dfe6172cab82984fa15a2b86d816c3
Signed-off-by: Rafael Franco <git@rafaelfranco.es>
Reviewed-on: https://review.coreboot.org/c/flashrom/+/94040
Reviewed-by: Anastasia Klimchuk <aklm@chromium.org>
Tested-by: build bot (Jenkins) <no-reply@coreboot.org>
Reviewed-by: Abdelkader Boudih <coreboot@seuros.com>