ANDROID: Add devfreq governor.h header to unsafe header.

To use devfreq driver, the governor stucture is essential
to register various governor to devfreq framework.
So adding the governor.h from driver/devfreq/ to the unsafe header.
This fix makes possible to include the header files for many vendor drivers.

Bug: 376618257
Signed-off-by: Konsu Lee <konsu.lee@samsung.com>
Signed-off-by: Hajun Sung <hajun.sung@samsung.com>
Change-Id: Ic7f9804c53d6c7f8e2388a12f4a66e04216240be