rcuscale: Allow rcuscale without RCU Tasks

Currently, a CONFIG_PREEMPT_NONE=y kernel substitutes normal RCU for
RCU Tasks. Unless that kernel builds rcuscale, whether built-in or as
a module, in which case RCU Tasks is (unnecessarily) built. This both
increases kernel size and increases the complexity of certain tracing
operations. This commit therefore decouples the presence of rcuscale
from the presence of RCU Tasks.

Signed-off-by: Paul E. McKenney <paulmck@kernel.org>

torture: Remove RCU_FAST_NO_HZ from rcuscale and refscale scenarios

All of the rcuscale and refscale scenarios that mention the Kconfig option
CONFIG_RCU_FAST_NO_HZ disable it. But this Kconfig option is disabled by
default, so this commit removes the pointless "CONFIG_RCU_FAST_NO_HZ=n"
lines from these scenarios.

Signed-off-by: Paul E. McKenney <paulmck@kernel.org>

rcuscale: Allow CPU hotplug to be enabled

It is no longer possible to disable CPU hotplug in many configurations,
which means that the CONFIG_HOTPLUG_CPU=n lines in rcuscale's Kconfig
options are just a source of useless diagnostics. In addition, rcuscale
doesn't do CPU-hotplug operations in any case. This commit therefore
changes these lines to read CONFIG_HOTPLUG_CPU=y.

Signed-off-by: Paul E. McKenney <paulmck@kernel.org>

rcuperf: Change rcuperf to rcuscale

This commit further avoids conflation of rcuperf with the kernel's perf
feature by renaming kernel/rcu/rcuperf.c to kernel/rcu/rcuscale.c, and
also by similarly renaming the functions and variables inside this file.
This has the side effect of changing the names of the kernel boot
parameters, so kernel-parameters.txt and ver_functions.sh are also
updated. The rcutorture --torture type was also updated from rcuperf
to rcuscale.

[ paulmck: Fix bugs located by Stephen Rothwell. ]
Reported-by: Ingo Molnar <mingo@kernel.org>
Signed-off-by: Paul E. McKenney <paulmck@kernel.org>