SystemUI: fix dpad arrow keys after rotation

We need to keep the saved visibilities of the side buttons separately
for both vertical and horizontal layouts because they can get out of
sync. For instance rotating a device when IME keys are shown, does not
guarentee that they will be shown after the rotation is finished.

Change-Id: I7cfe7dc941811b7663d965e4f08dd52a8c0fdea4
Signed-off-by: Roman Birg <roman@cyngn.com>