Allow Powerdown menu for devices other than M1

This is the corresponding modification to XBMC to renable shutdown option for M3.  Will only be necessary if you should to merge in the pull request to buildroot at:
https://github.com/Pivosgroup/buildroot-linux/pull/51

This renables Powerdown menu so S95-xbmc script has a chance to run and dismount drives and removable media.

On M3 users will have to physically remove power to power off.