power: qpnp-smbcharger: add option for charging unknown batteries

Currently, the qpnp-smbcharger is set to never charge unrecognized
batteries. However, certain devices do not yet have battery profiles
ready to be loaded into the fuel gauge. There should still be a way to
charge the battery without having a fuel gauge profile.

Add the devicetree property qcom,charge-unknown-battery in order to
disable this feature and charge any battery as long as a valid charger
is present.

Change-Id: I36004c58238de4baa807ae0ea92c4a29e810e496
Signed-off-by: Xiaozhe Shi <xiaozhes@codeaurora.org>