[flashrom] Restructure shutdown functions and remove global state

[Joursoir]

Hello everyone,

Today I had a first meeting with my mentor Anastasia. And I'm looking
forward to see Thomas as soon as possible. We've discussed our project
goals, initial tasks and current state of the code.

My next tasks:
1) Move all par masters to new API. It includes reducing the use of
static global variables by storing them in a specific programmer data
structure.
2) Introduce default shutdown function that can be very useful.
We already have a patch for it: https://review.coreboot.org/c/flashrom/+/54890

It will be done in small steps/commits. So I hope to send a first patch
soon.