spi25.c: Move spi_get_opcode_from_erasefn() to spi.c

Split spi_get_opcode_from_erasefn() out into spi.c to add support for
non spi25 flashes next.

Change-Id: Id654e998d0af2d3f5845336bb98b38d724519038
Signed-off-by: Thomas Heijligen <thomas.heijligen@secunet.com>
Original-Reviewed-on: https://review.coreboot.org/c/flashrom/+/67715
Original-Reviewed-by: Thomas Heijligen <src@posteo.de>
Original-Reviewed-by: Edward O'Callaghan <quasisec@chromium.org>
Reviewed-on: https://review.coreboot.org/c/flashrom-stable/+/72540
Reviewed-by: Nico Huber <nico.h@gmx.de>
Tested-by: build bot (Jenkins) <no-reply@coreboot.org>
2 files changed