qcom: battery: Raise parallel FCC above 500mA minimum

The existing parallel algorithm assumes FCC can go as low as
25mA on parallel charger. This is not always the case. SMB1355
has hardware logic that shuts it down if FCC is ever < 500mA
since it was designed as a slave charger.

Reorganize the parallel algorithm so that a minimum of 500mA
is assigned to SMB if parallel is to be enabled. The following
changes are included:

pl_disable_vote_callback is the ultimate function responsible
for distributing FCC and enabling/disabling parallel charger.

pl_fcc_vote_callback cast a vote to pl_disable_votable. Vote to
disable SMB when its share is below 500mA; otherwise vote to
enable.

Any input voltage or ICL change could cause SMB's share of FCC
to cross 500mA threshold, hence call FCC rerun_election.

Change-Id: I73295b84b08f118b2b74736a6079b58179e16acf
Signed-off-by: Harry Yang <harryy@codeaurora.org>