power: pmic-voter: add debug logs for votes

Add a name for each pmic votable registered, and add some debug logs
when votes are cast and when the final value is changed.

Change-Id: I0cce9c6140162d8409af4060ebc6247b18ddfa3a
Signed-off-by: Xiaozhe Shi <xiaozhes@codeaurora.org>
Signed-off-by: Abhijeet Dharmapurikar <adharmap@codeaurora.org>