spi25: Use common code for nbyte read/write and block erase

Upstream `commit 0ecbacbfca7f`.

BUG=chromium:478356
BRANCH=none
TEST=still builds

Change-Id: Ie246090e0f49f4dce50cdaed2b58be5d9e45075e
Signed-off-by: Edward O'Callaghan <quasisec@chromium.org>
Reviewed-on: https://chromium-review.googlesource.com/c/chromiumos/third_party/flashrom/+/1667512
Reviewed-by: Stefan Reinauer <reinauer@google.com>
3 files changed