cpufreq: Add boost frequency support in core

cpufreq: Add boost frequency support in core

This commit adds boost frequency support in cpufreq core (Hardware &
Software).
Some SoC (like Exynos4 - e.g. 4x12) allow setting frequency above
its normal operation limits. Such a mode shall be only used for a short
time.

Overclocking (boost) support is essentially provided by platform
dependent cpufreq driver.

This commit unifies support for SW and HW (Intel) overclocking solutions
in the core cpufreq driver. Previously the "boost" sysfs attribute was
defined at acpi driver code.
By default boost is disabled. One global attribute is available at:
/sys/devices/system/cpu/cpufreq/boost.

It only shows up when cpufreq driver supports overclocking.
Under the hood frequencies dedicated for boosting are marked with a
special flag (CPUFREQ_BOOST_FREQ) at driver's frequency table.
It is the user's concern to enable/disable overclocking with proper call to
sysfs.

Signed-off-by: Lukasz Majewski <l.majewski@samsung.com>
Signed-off-by: Myungjoo Ham <myungjoo.ham@samsung.com>
Changes for v6:
- Remove sysfs boost attribute when subsys_iterface_unregister() fails
- Move global boost_enabled variable from cpufreq.c to platform dependent
  struct cpufreq_driver
- pr_err() message is also printed when boost disable fails

Changes for v5:
- Rename cpufreq_boost_trigger_state_sw() to cpufreq_boost_enable_sw()
- Extent cpufreq_register_driver() to check if cpufreq driver provided
  boost_enable callback. If not provided, then use cpufreq_boost_enable_sw()
- Use single call to cpufreq_driver->enable_boost() with cpufreq driver
  provided callback or default SW boost enable routine
- Move pr_debug call to store_boost() from cpufreq_boost_trigger_state()
- Change the user_policy.max value when SW boost is toggled. It is necessary
  for proper operation of e.g. thermal subsystem.
- Add check if cpufreq_driver pointer is not NULL at
  cpufreq_boost_supported() routine
- Add EXPORT_SYMBOL_GPL for cpufreq_boost_supported() and
  cpufreq_boost_enabled()
- Remove extra check for cpufreq_boost_supported() at
  cpufreq_freq_table_cpuinfo()
- Explanation of show boost logic at show_available_freqs()
- Add cpufreq_set_boost_enabled() method to set initial value of boost_enabled
  global flag

Changes for v4:
- Remove boost parameter from cpufreq_frequency_table_cpuinfo() function
- Introduce cpufreq_boost_supported() method
- Use of cpufreq_boost_supported() and cpufreq_boost_enabled() to decide
  if frequency shall be skipped
- Rename set_boost_freq() to enable_boost()
- cpufreq_attr_available_freq() moved to freq_table.c
- Use policy list to get access to cpufreq policies
- Rename global boost flag (cpufreq_boost_enabled -> boost_enabled)
- pr_err corrected ( %sable)
- Remove sanity check at cpufreq_boost_trigger_state() entrance [to test if
  boost is supported]
- Use either HW (boost_enable) callback or SW managed boost
- Introduce new cpufreq_boost_trigger_state_sw() method to handle boost
  at SW.
- Protect boost_enabled manipulation with lock.

Changes for v3:
- Method for reading boost status
- Removal of cpufreq_frequency_table_max()
- Extent cpufreq_frequency_table_cpuinfo() to support boost parameter
- boost_supported flag added to cpufreq_driver struct
- "boost" sysfs attribute control flag removed
- One global flag describing state of the boost defined at cpufreq core
- Rename cpufreq_driver's low_level_boost field to set_boost_freq()
- Usage of cpufreq_sysfs_{remove|add}_file() routines

Changes for v2:
- Removal of cpufreq_boost structure and move its fields to cpufreq_driver
  structure
- Flag to indicate if global boost attribute is already defined
- Extent the pr_{err|debbug} functions to show current function names