erofs: remove WQ_CPU_INTENSIVE flag from unbound wq's

The documentation [1] says that WQ_CPU_INTENSIVE is "meaningless" for
unbound wq. I remove this flag from places where unbound queue is
allocated. This is supposed to improve code readability.

[1] https://www.kernel.org/doc/html/latest/core-api/workqueue.html#flags


Signed-off-by: Maksym Planeta <mplaneta@os.inf.tu-dresden.de>
[Gao Xiang: since the original treewide patch [2] hasn't been merged
            yet, handling the EROFS part only for the next cycle. ]
[2] https://lore.kernel.org/r/20200213141823.2174236-1-mplaneta@os.inf.tu-dresden.de
Link: https://lore.kernel.org/r/20200731024049.16495-1-hsiangkao@aol.com


Reviewed-by: Chao Yu <yuchao0@huawei.com>
Signed-off-by: Gao Xiang <hsiangkao@redhat.com>