cpufreq: Make the "scaling_governor" sysfs node pollable

A userspace module programs different qos-rules depending on the
governor running in the system. Make the governor node
pollable, so that the userspace module can be triggered when
the value of the governor changes.

change-Id: Ic89c77c7d16b0f8954d59a211612e9a8e98a2c28
Signed-off-by: Amar Singhal <asinghal@codeaurora.org>

Conflicts:

	drivers/cpufreq/cpufreq.c
drivers: cpufreq: Send a uevent when governor changes

 * Useful so userspace tools can reconfigure.

Change-Id: Ib423910b8b9ac791ebe81a75bf399f58272f64f2
cpufreq: sync interactive gov with android-3.0