Added sysfs option to set screen_on_min_freq
With this option, the certain lack of smoothness can be counteracted when scaling_min_freq is set very low (e.g. to 192 MHz). Thanks to this option, battery savings granted by the low scaling_min_freq can be achieved, without any negative effects to the user.
The sysfs path is located at: /sys/devices/system/cpu/cpu0/cpufreq/screen_on_min_freq

Conflicts:
	arch/arm/mach-omap2/omap2plus-cpufreq.c