soc: qcom: mem-offline: log additional time stats

With active-mode memory offlining, it would be helpful to track the
total Online and Offline times of each blocks and determine percentage
of time they have been in that state.
This patch adds the below additional stats:
   - current state of each blocks.
   - total Online and Offline time of each blocks.
   - percentage of total system runtime that blocks were in Online
     and Offline state.
   - total overall percentage of time all blocks were in Online
     and Offline state.

Also, change the sysfs node from 'perf_stats' to 'stats'.

Change-Id: Ie18ad68194df8c7702dc496821c4f680d15486ce
Signed-off-by: Sudarshan Rajagopalan <sudaraja@codeaurora.org>