power: qpnp-smbcharger: Implement a voter class for the pmic clients

Since there are many clients that control common resources like
input/battery current limit, implement a voting scheme to vote on
these resource values.

Change-Id: I2e7c114a8985030d3e54e7c98687c94aeb3c3c73
Signed-off-by: Devesh Jhunjhunwala <deveshj@codeaurora.org>