power: qpnp-fg: disable ESR measurements during sleep

Currently, the fuelgauge hardware issues ESR pulses to help measure the
real resistance of the battery. However, this can raise the rock bottom
current draw of the device.

Since the ESR measurements are necessary in low current conditions,
disable them when going into suspend.

Change-Id: I7ef75811f4378b326d0d438ba7aa6fc87158be30
Signed-off-by: Xiaozhe Shi <xiaozhes@codeaurora.org>