target/riscv: hard reset DTM if dmistat is busy

Due to certain reasons, the DMI scan is busy,
leading to a timeout and exit. When restarting
OpenCD, a hard reset of the DTM is required.

Author: lz-bro

src/target/riscv/riscv-013.c

@@ -2016,6 +2016,12 @@ static int examine(struct target *target)
 		return ERROR_FAIL;
 	}
 
+	if (get_field(dtmcontrol, DTM_DTMCS_DMISTAT) != DTM_DMI_OP_SUCCESS) {
+		if (dtmcs_scan(target->tap, DTM_DTMCS_DTMHARDRESET,
+				NULL /* discard result */) != ERROR_OK)
+			return ERROR_FAIL;
+	}
+
 	riscv013_info_t *info = get_info(target);
 
 	info->index = target->coreid;