power: qpnp-vm-bms: Disable IBAT averaging at lower temperatures

At lower battery temperatures the SOC drops much faster due to
an increase in RBAT. This drop in SOC is rate-limited by IBAT
averaging and UUC smoothening features. If this drop in SOC
is not managed in the software it may cause the device to UVLO.
Handle this by disabling the rate-limiting features at lower
battery temperatures. The temperature threshold can be specified
by DT or it defaults to 0 degC.

While at it, also add a DT parameter to specify the number of
IBAT samples to average for calculating the estimated IBAT used for
UUC smoothening. This adds flexibility to choose between SOC linearity
and accuracy for the cut-off voltage. Lower the #samples, better is
the accuracy to power-off at the cutoff voltage.

Change-Id: I78f318feed764392102ff484e11487745e3f8132
Signed-off-by: Anirudh Ghayal <aghayal@codeaurora.org>