UPSTREAM: fsverity: Remove WQ_UNBOUND from fsverity read workqueue

WQ_UNBOUND causes significant scheduler latency on ARM64/Android.  This
is problematic for latency sensitive workloads, like I/O
post-processing.

Removing WQ_UNBOUND gives a 96% reduction in fsverity workqueue related
scheduler latency and improves app cold startup times by ~30ms.
WQ_UNBOUND was also removed from the dm-verity workqueue for the same
reason [1].

This code was tested by running Android app startup benchmarks and
measuring how long the fsverity workqueue spent in the runnable state.

Before
Total workqueue scheduler latency: 553800us
After
Total workqueue scheduler latency: 18962us

[1]: https://lore.kernel.org/all/20230202012348.885402-1-nhuck@google.com/



Signed-off-by: Nathan Huckleberry <nhuck@google.com>
Fixes: 8a1d0f9cacc9 ("fs-verity: add data verification hooks for ->readpages()")
Cc: stable@vger.kernel.org
Link: https://lore.kernel.org/r/20230310193325.620493-1-nhuck@google.com


Signed-off-by: Eric Biggers <ebiggers@google.com>

Bug: 258554362
(cherry picked from commit f959325e6ac3f499450088b8d9c626d1177be160)
Change-Id: I13f74e0df913894938969582604947e8a1fc51a3
Signed-off-by: Eric Biggers <ebiggers@google.com>