power: qpnp-smbcharger: enable the fastchg interrupt

Enable the fastcharge interrupt (precharge-to-fastcharge threshold
interrupt) in order to allow the charger driver to update the battery
power supply with the charging status whenever the device starts
charging.

Change-Id: I354fe73198f9d1dc23b51845d5d17f6ad7f477bf
Signed-off-by: Xiaozhe Shi <xiaozhes@codeaurora.org>