block: fix inaccurate io_ticks by set 'precise_iostat'

hulk inclusion
category: bugfix
bugzilla: https://gitee.com/openeuler/kernel/issues/I5X6RT


CVE: NA

--------------------------------

After introducing commit 5b18b5a7 ("block: delete part_round_stats
and switch to less precise counting"), '%util' accounted by iostat
will be over reality data. In fact, the device is quite idle, but
iostat may show '%util' as a big number (e.g. 50%). It can produce by fio:

fio --name=1 --direct=1 --bs=4k --rw=read --filename=/dev/sda \
	   --thinktime=4ms --runtime=180
We fix this by using a switch(precise_iostat=1) to control whether or not
acconut ioticks precisely.

fixes: 5b18b5a7 ("block: delete part_round_stats and switch to less precise counting")
Signed-off-by: Zhang Wensheng <zhangwensheng5@huawei.com>
Signed-off-by: Yu Kuai <yukuai3@huawei.com>
Reviewed-by: Jason Yan <yanaijie@huawei.com>
Signed-off-by: Zheng Zengkai <zhengzengkai@huawei.com>