urcu: make the code of urcu-qsbr as normal urcu

urcu-qsbr's read site's quiescence is much longer than normal urcu ==>
synchronize_rcu() is much slower ==>
rcu_gp_ctr is updated much less ==>
the whole urcu-qsbr will not be slowed down by false sharing of rcu_gp_ctr.

But this patch makes sense to keep the code of urcu-qsbr like normal urcu,
better readability and maintenance.

Test: (4*6 CPUs)
Before patch:
[root@localhost userspace-rcu]# ./tests/test_urcu_qsbr 20 1 20
SUMMARY ./tests/test_urcu_qsbr    testdur   20 nr_readers  20 rdur      0 wdur      0 nr_writers   1 wdelay      0 nr_reads  65498297587 nr_writes      2000665 nr_ops  65500298252
[root@localhost userspace-rcu]# ./tests/test_urcu_qsbr 20 1 20
SUMMARY ./tests/test_urcu_qsbr    testdur   20 nr_readers  20 rdur      0 wdur      0 nr_writers   1 wdelay      0 nr_reads  67218079467 nr_writes      1981593 nr_ops  67220061060

After patch
./tests/test_urcu_qsbr 20 1 20
SUMMARY ./tests/test_urcu_qsbr    testdur   20 nr_readers  20 rdur      0 wdur      0 nr_writers   1 wdelay      0 nr_reads  67473798999 nr_writes      1999151 nr_ops  67475798150
[root@localhost userspace-rcu]# ./tests/test_urcu_qsbr 20 1 20
SUMMARY ./tests/test_urcu_qsbr    testdur   20 nr_readers  20 rdur      0 wdur      0 nr_writers   1 wdelay      0 nr_reads  67065521397 nr_writes      1993956 nr_ops  67067515353

Signed-off-by: Lai Jiangshan <laijs@cn.fujitsu.com>
Signed-off-by: Mathieu Desnoyers <mathieu.desnoyers@efficios.com>