flashrom.c: implement chip restore callback registration

Allows drivers to register a function that gets called to
reset the chip state once programming has finished. This is
used by the s25f driver added in a following patch.

BUG=b:153800073
BRANCH=none
TEST=builds

Change-Id: I2a522dc1fd3952793fbcad70afc6dd43850fbbc5
Signed-off-by: Nikolai Artemiev <nartemiev@google.com>
---
M flash.h
M flashrom.c
2 files changed, 41 insertions(+), 0 deletions(-)