cpufreq:acpi:x86: Adjust the acpi-cpufreq.c code to work with common boost solution

cpufreq:acpi:x86: Adjust the acpi-cpufreq.c code to work with common boost solution

The Intel's hardware based boost solution driver has been changed to cooperate with
common cpufreq boost framework.

The global sysfs boost attribute entry code (/sys/devices/system/cpu/cpufreq/boost)
has been moved to a core cpufreq code. This attribute is now only visible,
when cpufreq driver supports it.

The _store_boost() function has been redesigned to be used as enable_boost
callback.

Signed-off-by: Lukasz Majewski <l.majewski@samsung.com>
Signed-off-by: Myungjoo Ham <myungjoo.ham@samsung.com>
Changes for v6:
- Use boost_enabled flag defined at acpi_cpufreq_driver to store information
  about boost state
- Instead of using cpufreq_set_boost_enabled(), modify the boost_enable in
  the acpi driver code

Changes for v5:
- Remove acpi-cpufreq's boost_enabled global flag and reuse one defined at
  cpufreq core

Changes for v4:
- add _store_boost to acpi_cpufreq_driver structure

Changes for v3:
- Bring back boost_enabled as a global flag
- Move boost_supported to cpufreq_driver structure

Changes for v2:
- Replace boost_enabled and boost_supported global flags with proper entries
at struct cpufreq_driver.
- Removal of struct cpufreq_boost