icnss: Enable platform device to be a wakeup source

Currently platform device is not enabled as a wakeup source, so
notifying the PM core for a wakeup event action will be no-op.
Hence enable it during driver probe.

CRs-Fixed: 2058010
Change-Id: Iefe5bcd4b498a9f02fca001ebcf8ad484f443217
Signed-off-by: Yuanyuan Liu <yuanliu@codeaurora.org>