flash/nor/fespi: algorithm, large address, errors

* Move more smarts into the target algorithm code, and rewrite that in C
  so it's easier to understand/maintain.
* Support >24-bit addresses.
* Check for errors.

Change-Id: I3b1a143589fe6defafb8f95820aa682acc9646e7
Signed-off-by: Tim Newsome <tim@sifive.com>
Reviewed-on: https://review.openocd.org/c/openocd/+/6679
Tested-by: jenkins
Reviewed-by: Tomas Vanek <vanekt@fbl.cz>