power: qpnp-smbcharger: support flash current prediction

There are certain usecases such as the camera flash that can create
large dips on VPH power due to how much current they can draw. It is
vital to limit the current consumption on these usecases to avoid having
the phone power pulled down below a threshold that can cause system
instabilities.

Predict the amount of current available to be drawn by the device using
the estimated battery open circuit voltage, the battery current, the
estimated battery resistance, and the buck efficiency and report this as
a power supply property for consumers to use for current limiting.

Also, add the device tree property qcom,rparasitics-uohm as a
configurable parameter to help estimate the maxium battery current by
defining the amount of parasitic resistance in the board.

Change-Id: Iaf44861acf6093f48aeea20718435422258149b4
Signed-off-by: Xiaozhe Shi <xiaozhes@codeaurora.org>