flashchips.c: Add GD25Q256D from downstream

Take definition of GD25Q256D from ChromiumOS repository.

This chip was added in `commit 0c38355c` by dlaurie@google.com
2019-03-17.

Signed-off-by: Alan Green <avg@google.com>
Change-Id: I79d4ed48aa9126a8a6ce455a9564451346195b8f
Reviewed-on: https://review.coreboot.org/c/flashrom/+/35480
Tested-by: build bot (Jenkins) <no-reply@coreboot.org>
Reviewed-by: Edward O'Callaghan <quasisec@chromium.org>
2 files changed