power: qpnp-fg: lower default cutoff and empty voltages

Lower the default cutoff and empty voltages in the fuel gauge driver in
order to allow the device to draw more charge out of the battery before
shutting down.

CRs-Fixed: 799661
Change-Id: Ie681407faaa1de8e1f9ae15b4f81bbf40912e884
Signed-off-by: Xiaozhe Shi <xiaozhes@codeaurora.org>