u8500-common: set screen off animation style to fade out

since the LCD backlight does not actually fade out, it causes the LCD backlight to stay on a little while after the elctron beam goes off. this makes the electron beam will look pretty ugly. changing the default screen off animation style to fade out makes it look just that much subtler and pleasing to the eye.

Change-Id: Ie325a27c09bf0224cf28501945b8605e5e012ba1
Signed-off-by: Zhao Wei Liew <zhaoweiliew@gmail.com>