BACKPORT: FROMGIT: rcu: Refactor code a bit in rcu_nocb_do_flush_bypass()

This consolidates the code a bit and makes it cleaner. Functionally it
is the same.

(cherry picked from commit 9121723696c063c1bee8d8c0f452ae8010a671e4
 https://git.kernel.org/pub/scm/linux/kernel/git/paulmck/linux-rcu.git

 rcu/next)

(Backport:
 Patched file name is different upstream.)

BUG=b:222463781
TEST=powerIdle lab tests.

Reported-by: Paul E. McKenney <paulmck@kernel.org>
Signed-off-by: Joel Fernandes (Google) <joel@joelfernandes.org>
Signed-off-by: Joel Fernandes <joelaf@google.com>
Signed-off-by: Parshuram Sangle <parshuram.sangle@intel.corp-partner.google.com>
Reviewed-on: https://chromium-review.googlesource.com/c/chromiumos/third_party/kernel/+/3965072


Reviewed-by: Ross Zwisler <zwisler@google.com>
Change-Id: I5bfa65d68d188bd9659c28d6ae9d89db00ab6cf6
Reviewed-on: https://chromium-review.googlesource.com/c/chromiumos/third_party/kernel/+/4069541