AudioManager: make swap volume buttons RTL aware

The layout of the volume panel is already RTL aware...the problem is
if it is in landscape and the buttons are swapped they go into opposite
direction then the volume panel.

So this swap should only happen on LTR languages and RTL should be left
like it is.

So both LTR and RTL have it logical.

Change-Id: Ie5fbe3085b40ad35814f53ed19736d7800dad78e