linux-yocto-rt/5.4: fix 5.4-stable caused build breakage

5.4-stable included a backport of:

   Author: Eric W. Biederman <ebiederm@xmission.com>
   Date:   Thu Dec 3 14:11:13 2020 -0600

     rwsem: Implement down_read_interruptible

     [ Upstream commit 31784cff7ee073b34d6eddabb95e3be2880a425c ]

     In preparation for converting exec_update_mutex to a rwsem so that
     multiple readers can execute in parallel and not deadlock, add
     down_read_interruptible.  This is needed for perf_event_open to be
     converted (with no semantic changes) from working on a mutex to
     wroking on a rwsem.

Signed-off-by: Eric W. Biederman <ebiederm@xmission.com>
Signed-off-by: Peter Zijlstra (Intel) <peterz@infradead.org>
     Link: https://lkml.kernel.org/r/87k0tybqfy.fsf@x220.int.ebiederm.org


Signed-off-by: Sasha Levin <sashal@kernel.org>

We implement a -rt variant to fix the build issues.

Signed-off-by: Bruce Ashfield <bruce.ashfield@gmail.com>
Signed-off-by: Richard Purdie <richard.purdie@linuxfoundation.org>
(cherry picked from commit e610fb7c)
Signed-off-by: Steve Sakoman <steve@sakoman.com>