programmer: Smoothen register_opaque_master() API

It was impossible to register a const struct opaque_master that would
point to dynamically allocated `data`. Fix that so that we won't
have to create more mutable globals.

BUG=b:185191942
TEST=builds

Change-Id: Id3adb4cf04ae04dbe87ddb96f30871cb5f7c8ff0
Signed-off-by: Anastasia Klimchuk <aklm@chromium.org>
Reviewed-on: https://review.coreboot.org/c/flashrom/+/54170
Reviewed-by: Edward O'Callaghan <quasisec@chromium.org>
Reviewed-by: Nico Huber <nico.h@gmx.de>
Tested-by: build bot (Jenkins) <no-reply@coreboot.org>
5 files changed