Enable StatusBar Brightness control for tablets.

Currently, tablets are specifically forbidden to enable
brightness control from the status bar. I believe this is
a relic of cm-9 and cm-10 when tablets didn't have a
status bar.
This us a convenient feature that should be a user option
for all devices.

Change-Id: I198feb53966e42a26616aaa490b20759b77a22fc
Merge remote-tracking branch 'cm/cm-11.0' into HEAD