ARM: add auto hotplug driver

auto_hotplug: enable the min_online_cpus value
Use a module_param_cb to set the minimum number of online CPUs when the screen is on.
The values are between 1-4.
usage:
echo '1' > /sys/module/auto_hotplug/parameters/min_online_cpus

auto_hotplug: some tweaks
Several tweaks to try to improve battery life.

Fix up some various naming issues after inclusion of max_online_cpus code

Francisco is right, onlining all cores is a nice workaround for the real problem.
Onlining all cores using the driver's framework.
Some whitespace cleanup.
cpufreq: Retain only online cpus in managed_policy->cpus

cpufreq's handling of cpu online event can incorrectly initialize
managed_policy->cpus to include offline cpus. This causes cpufreq
governors to include offline cpus in their idle time computation, which
causes frequency to shoot up beyond normal levels (on systems where 2 or
more cpus need to be synchronized wrt frequency change).

This frequency shootup was not seen prior to commit 21111be8 which
changed idle time accounting for offline cpus. Prior to commit 21111be8,
idle time statistics for offline cpus would include their offline time
as well. Post commit 21111be8, offline time is not included in a cpu's
idle time statistics.

As a result, ondemand (or other cpufreq) governors would see unchanged
idle time for offline cpus, causing them to interpret those (offline)
cpus as 100% busy, which is wrong.

This patch fixes the issue by modifying cpufreq's hotplug handling to
retain only online cpus in managed_policy->cpus field. cpufreq governors
would then skip such offline cpus from idle time calculations.

Change-Id: Id2eba8c0ec3367609369b2e42a4e1386ff2e7ab5
Signed-off-by: Srivatsa Vaddagiri <vatsa@codeaurora.org>
Signed-off-by: Francisco Franco <franciscofranco.1990@gmail.com>
smp: patches from mainline 3.5 to hopefully help with hotplug
efficiency

Thomas Gleixner's generic-idle patches:

smp: Add task_struct argument to __cpu_up()
Preparatory patch to make the idle thread allocation for secondary
cpus generic.
http://git.kernel.org/?p=linux/kernel/git/tip/tip.git;a=commit;h=8239c25f47d2b318156993b15f33900a86ea5e17

smp: Add generic smpboot facility
Start a new file, which will hold SMP and CPU hotplug related generic
infrastructure.
http://git.kernel.org/?p=linux/kernel/git/tip/tip.git;a=commit;h=38498a67aa2cf8c80754b8d304bfacc10bc582b5

smp: Provide generic idle thread allocation
All SMP architectures have magic to fork the idle task and to store it
for reusage when cpu hotplug is enabled. Provide a generic
infrastructure for it.
Create/reinit the idle thread for the cpu which is brought up in the
generic code and hand the thread pointer to the architecture code via
__cpu_up().
Note, that fork_idle() is called via a workqueue, because this
guarantees that the idle thread does not get a reference to a user
space VM. This can happen when the boot process did not bring up all
possible cpus and a later cpu_up() is initiated via the sysfs
interface. In that case fork_idle() would be called in the context of
the user space task and take a reference on the user space VM.
http://git.kernel.org/?p=linux/kernel/git/tip/tip.git;a=commit;h=29d5e0476e1c4a513859e7858845ad172f560389

arm: Use generic idle thread allocation
http://git.kernel.org/?p=linux/kernel/git/tip/tip.git;a=commit;h=84ec6d5796e095e2f8698bd2b5d33849ed26d9e2
Signed-off-by: Francisco Franco <franciscofranco.1990@gmail.com>