power: vm-bms: Initialize the last_soc at power-on

At power-on initialize the last_soc (reported SOC) with
the shutdown SOC and set the calculated_soc to shutdown
OCV based SOC. This makes sure that we catch-up with
the calculated_soc (if charging) based on the scaling logic.

While at it, make the low_soc_check unconditional for the
fifo_length to get updated even when calculated soc has
not changed (catch-up during boot). Also, execute the
monitor soc work immediately at power-on.

CRs-Fixed: 665487
Change-Id: Id3bfc51163fb7336560508fd8c270db17e0181b6
Signed-off-by: Anirudh Ghayal <aghayal@codeaurora.org>