usb: dwc3-msm: Enable pwr_evt_irq for wakeup after LPM is done

Platforms using Synopsys SS phy are enabling pwr_evt_irq for
wakeup events in host mode as a part of dwc3_msm_suspend, but
before all the resources have been relinquished. So it is
possible that an IRQ is fired before dwc->in_lpm could be set to
1. Because of this, the pwr_event_handler will try to read
STAT_REG without issuing resume_work leading to unclocked access.
Fix this by enabling pwr_evt_irq only after in_lpm flag is set to
1, hence ensuring resume when the irq is fired.

Change-Id: I9772f427ecd10c2922c998cf0d57734362413051
Signed-off-by: Ajay Agarwal <ajaya@codeaurora.org>