Don't try to restore Set on Boot settings before decrypting

If encryption is enabled, BootReceiver will not be able to find
the performance preferences and set sys.{cpufreq,iosched}.restored
to true, inhibiting the second invocation after decryption from
doing so (because it thinks that the settings were already restored).
This patch fixes that by not attempting to restore settings while
/data is not yet decrypted.

Change-Id: I8bfe1cda856f344995e5528ebfb9c894701b395e