badblocks: add more helper structure and routines in badblocks.h

This patch adds the following helper structure and routines into
badblocks.h,
- struct badblocks_context
  This structure is used in improved badblocks code for bad table
  iteration.
- BB_END()
  The macro to calculate end LBA of a bad range record from bad
  table.
- badblocks_full() and badblocks_empty()
  The inline routines to check whether bad table is full or empty.
- set_changed() and clear_changed()
  The inline routines to set and clear 'changed' tag from struct
  badblocks.

These new helper structure and routines can help to make the code more
clear, they will be used in the improved badblocks code in following
patches.

Signed-off-by: Coly Li <colyli@suse.de>
Reviewed-by: Xiao Ni <xni@redhat.com>
Cc: Dan Williams <dan.j.williams@intel.com>
Cc: Geliang Tang <geliang.tang@suse.com>
Cc: Hannes Reinecke <hare@suse.de>
Cc: Jens Axboe <axboe@kernel.dk>
Cc: NeilBrown <neilb@suse.de>
Cc: Vishal L Verma <vishal.l.verma@intel.com>
Acked-by: Geliang Tang <geliang.tang@suse.com>
Link: https://lore.kernel.org/r/20230811170513.2300-2-colyli@suse.de


Signed-off-by: Jens Axboe <axboe@kernel.dk>