target: Update messages connected with examine

[kr-sc]

Move examine_attempted flag to target struct to make it target specific.

Info messages for retry and Error messages for failure added.

P.S. I have to request this patch here because of https://review.openocd.org/c/openocd/+/6964. There is no such patch in upstream openocd repo.

[timsifive]

Looks OK.

[en-sc]

@kr-sc , @timsifive, unfortunately, this needs to be reverted. The implementation is buggy.

We have target_examine() function:

    for (target = all_targets; target; target = target->next) {
        /* defer examination, but don't skip it */
        if (!target->tap->enabled) {
            jtag_register_event_callback(jtag_enable_callback,
                    target);
            continue;
        }
        if (target->defer_examine)
            continue;

        target->examine_attempted = true;

This function is called only once. From src/openocd.c. So, the original intention for the variable is just to mark that this function was called. I guess that this may result in subtle errors, since the condition for:

    if (retval != ERROR_OK && target->examine_attempted) {                                        
        target_reset_examined(target);                                                              
        retval = target_examine_one(target);                                                        
        if (retval != ERROR_OK) {                                                                   
           LOG_TARGET_DEBUG(target, "Polling again in %dms",                                         
              target->backoff.interval);                                                              
           return retval;                                                                            
         }                                                                                           
    }

Will never be true for the targets that had a deferred examine.

[kr-sc]

@en-sc is right, unfortunately
mr with revert here #934