ueventd: Adds permission to ueventd to access sysfs file

Need this for changing max_cpufreq for the low power mode.

Denials:
type=1400 audit(1398818907.151:48): avc:  denied  { relabelfrom } for
pid=129 comm="ueventd" name="scaling_max_freq" dev="sysfs" ino=19866
scontext=u:r:ueventd:s0 tcontext=u:object_r:sysfs:s0 tclass=file

type=1400 audit(118521.050:11): avc:  denied  { setattr } for  pid=130
comm="ueventd" name="scaling_min_freq" dev="sysfs" ino=9178
scontext=u:r:ueventd:s0 tcontext=u:object_r:sysfs_devices_system_cpu:s0
tclass=file

Change required for Change-Id: Ibe0b4aaf3db555ed48e89a7fcd0c5fd3a18cf233

Change-Id: I93feee65b1535ac048acf3bc7fba9f5d1bdb2bd2
Signed-off-by: Ruchi Kandoi <kandoiruchi@google.com>