power: qpnp-fg: wait for the battery psy when loading profile

Currently the fuel gauge driver needs the charger to stop charging while
doing a profile reload. However, it is not guaranteed that the fuel
gauge driver probes after the charger driver probes and registers the
battery power supply. This can cause an issue where the battery is still
being charged when doing a profile reload, creating issues with the fuel
gauge SOC upon a cold boot.

Fix this by waiting for the battery power supply to load before loading
a profile.

Change-Id: I23ce2bc0f70390ac41d7a2130b33428c18d8ddba
Signed-off-by: Xiaozhe Shi <xiaozhes@codeaurora.org>