rootdir: init.rc: Fix for "add_tid_to_cgroup failed to write" warnings

Logcat is full of warnings like:

 W/SchedPolicy( 2013): add_tid_to_cgroup failed to write '2371' (Permission denied); policy=1

This is fixed by giving /dev/cpuctl group write permissions, which was
surely the original intention of the init.rc setup as this is done for
the sub-directories it creates.

This fixes bug launchpad bug #1037611

Change-Id: I47ff539ef4dd9922aba0be67dbf8bd4f0a234163
Signed-off-by: Jon Medhurst <tixy@linaro.org>