power: qpnp-vm-bms: Manage state-change IRQ only during charging

Managing (enable/disable) the state-change IRQ during suspend/resume
may cause this IRQ trigger very frequently. The real use of this IRQ
is only during charging, hence enable/disable the IRQ only when we
start charging/discharging.

Change-Id: I962d442520315be41fdab860e71963bf49fa29bf
Signed-off-by: Anirudh Ghayal <aghayal@codeaurora.org>