dwc3_msm: Enable POWER EVENT IRQ as wakeup source

Power event irq is required to enable as wakeup source with MPM
pin configuration to support bus supsend/resume functionality
with XOSD. As this change enables power event irq wakeup source,
it is must to have entry for <MPM pin, Power event IRQ> in
platform's pm device tree, otherwise this would prevent device
going into XOSD.

CRs-Fixed: 727450
Change-Id: Ib36cdb5f72dffbabde2b343c655519e18b03730f
Signed-off-by: Mayank Rana <mrana@codeaurora.org>