dt-bindings: qpnp-fg-gen4: Support ESR calibration during discharging

Add support to configure ESR calibration or measurements done
only during discharging. This configuration works mutually
exclusive to ESR fast calibration with the required parameters
specified through "qcom,fg-esr-calib-dischg" property.

Change-Id: I976f42de818ad1b7abd62c7856d29987b909a3a3
Signed-off-by: Subbaraman Narayanamurthy <subbaram@codeaurora.org>