power: qpnp-smbcharger: add parallel charging support

Add functionality for enabling an external parallel charger whenever
AICL completes with enough input current limit.

When the parallel charger is enabled, it should allow a portion of the
current through a different charge path.

Change-Id: I29cb6c3777d23d1d9964447420fd59294c8d7898
Signed-off-by: Xiaozhe Shi <xiaozhes@codeaurora.org>