Add prepare/finish_access() hooks for chip drivers

Some of the arrangements we perform in prepare_flash_access()
are actually specific to the flash chip. Allow to clean that
up by adding respective hooks into `struct flashchip`.

Change-Id: Iff79ba3d190dba04ecf58c5c53faa428bf592bdf
Signed-off-by: Nico Huber <nico.h@gmx.de>
Reviewed-on: https://review.sourcearcade.org/c/flashprog/+/72516
2 files changed