power: qpnp-fg: add POWER_SUPPLY_RESISTANCE_ID support

Add support to expose the battery id resistance in ohms
via the power supply framework.

As part of this change, add the qcom,fg-batt peripheral
node to allow the driver to check if a valid battery
ID reading is available.

Change-Id: I9aa51a8ad42b59bef945950de231aacaaf947cd3
Signed-off-by: David Keitel <dkeitel@codeaurora.org>