Revert "Revert "add auto hotplug""

BT seems fine with HotPlug now in the 4.4 rebase.. so lets add this back as it will help with battery life etc.

This reverts commit a238d7ba0b0cdef8df20b5aba4f3667f6d36c4d4.

Change-Id: Ife7d3ee1d5b38125ece1f38fd9be05b32c6743a6