dt-bindings: qpnp-fg-gen4: support configuring filtered battery current

To qualify the capacity learning algorithm start, add support to
configure filtered battery current threshold.

Change-Id: If8be108c1879572a4fafe62bb29afdb21fb1d9fe
Signed-off-by: Subbaraman Narayanamurthy <subbaram@codeaurora.org>