cpupower: Add turbo-boost support in cpupower

If boost sysfs (/sys/devices/system/cpu/cpufreq/boost) file is present
turbo-boost is feature is supported in the hardware. By default this
feature should be enabled. But to disable/enable it write to the sysfs
file. Use the same to control this feature via cpupower.

To enable:
cpupower set --turbo-boost 1

To disable:
cpupower set --turbo-boost 0

Acked-by: Huang Rui <ray.huang@amd.com>
Reviewed-by: Gautham R. Shenoy <gautham.shenoy@amd.com>
Reviewed-by: Mario Limonciello <mario.limonciello@amd.com>
Signed-off-by: Wyes Karny <wyes.karny@amd.com>
Tested-by: Perry Yuan <Perry.Yuan@amd.com>
Signed-off-by: Shuah Khan <skhan@linuxfoundation.org>