recovery.te: Allow writing to sysfs_devices_system_cpu.

recovery (update_binary) may need to set up cpufreq during an update.

avc:  denied  { write } for  pid=335 comm="update_binary" name="scaling_max_freq" dev="sysfs" ino=7410 scontext=u:r:recovery:s0 tcontext=u:object_r:sysfs_devices_system_cpu:s0 tclass=file permissive=0

Bug: 32463933
Test: Build a recovery image and apply an OTA package that writes to
      /sys/devices/system/cpu/cpu0/cpufreq/scaling_max_freq.

Change-Id: Ia90af9dd15e162dd94bcd4722b66aa296e3058c5