Expose /dev/hw_random to group "system".

This is needed to let EntropyMixer (runs inside system_server) read
from /dev/hw_random.

Change-Id: Ifde851004301ffd41b2189151a64a0c5989c630f
ueventd: Add rules for governors and cpufreq

This change requires a kernel patch in cpufreq to work.

Change-Id: I6281645291ca4516748f65d0799e14971c5fb2ea