Fix the infamous Music/sdcard/FPU corruption bug.

In low power cpuidle states, the FPU registers get corrupted. By calling
cpu_pm_enter, the VFP module gets notified so that it saves the FPU state and
restores it from RAM the next time a thread uses it.
    
See http://forum.xda-developers.com/showthread.php?p=57637134 to http://forum.xda-developers.com/showthread.php?p=57643086 (zeitferne is my XDA name, as you can infer from my links to gists there).


Obligatory WARNING: Although the patch is reasonably well tested, I just entered this manually in github's online editor. Refer to the linked posts for links to the patchset. However, you have already included all required mainline commits, so I thought this additional three-line change should be doable w/o downloading the full repository.