devfreq: Account only powered time in trans_stat

This patch modifies devfreq to account only the time a device is
powered in trans_stat. In addition, this patch also fixes a race
in trans_stat maintenance in cases where the node is readed at
the same time the transition table is being updated by frequency
re-estimation.

Change-Id: I6e4341317b6dda88d69028c9f67785400e5a7a65
Signed-off-by: Arto Merilainen <amerilainen@nvidia.com>
Reviewed-on: http://git-master/r/435174
Reviewed-by: Automatic_Commit_Validation_User
Reviewed-by: Diwakar Tundlam <dtundlam@nvidia.com>
Reviewed-by: Prajakta Gudadhe <pgudadhe@nvidia.com>
Reviewed-by: Samuel Russell <samuelr@nvidia.com>
Tested-by: Samuel Russell <samuelr@nvidia.com>
Reviewed-by: Ilan Aelion <iaelion@nvidia.com>
Signed-off-by: Jake Weinstein <xboxlover360@gmail.com>
Devfreq: add back comments and use interruptable waits