power: qpnp-fg-gen4: Support OCV based step charging in TTF algorithm

Currently TTF algorithm support Vbatt based step charging, but since
oscillation in Vbatt is high when the load changes abruptly we have
moved to OCV based step charging. Add support for OCV based step charging
when TTF algorithm queries for mode and OCV value.

Change-Id: Iefffc864ba362aed53c1b486c25731a140a5b000
Signed-off-by: Sahil Chandna <chandna@codeaurora.org>
Signed-off-by: Subbaraman Narayanamurthy <subbaram@codeaurora.org>