cpufreq / boost: Kconfig: Support for software-managed BOOST

cpufreq / boost: Kconfig: Support for software-managed BOOST

Add CONFIG_CPU_FREQ_BOOST_SW Kconfig option such that software-managed
boost is enabled only after selecting "EXYNOS Frequency Overclocking -
Software".  It also depends on the thermal subsystem to be compiled in,
which is necessary for disabling boost and cooling down the device when
overheating is detected.

Software-managed boost _MUST_ _NOT_ be enabled without thermal subsystem
with properly defined overheating temperature thresholds.

This option doesn't affect the x86's hardware-driven boost support
in the acpi-cpufreq driver.

Signed-off-by: Lukasz Majewski <[email protected]>
Signed-off-by: Myungjoo Ham <[email protected]>
Acked-by: Viresh Kumar <[email protected]>
[rjw: Subject and changelog]
Signed-off-by: Rafael J. Wysocki <[email protected]>