Add rfkill permissions

Seems to be needed by the Wi-Fi driver; I'm getting this in logcat:

I/wpa_supplicant( 5765): rfkill: Cannot open RFKILL control device

Based on https://github.com/arco/android_device_htc_buzz/commit/46070bcd0a0658e655c8e71d7c18f4878eb47e9d