wcnss: Synchronize request_firmware() with suspend

Register for PM notifiers to avoid calling into request_firmware()
when the suspend/resume is in progress. Soon after a subsystem restart,
device can go to suspend mode, and wakeup when WCNSS opens the SMD
port to start NV download. So make sure that userspace is fully thawed
before starting NV download.

Change-Id: Iec0b742fd4c4bc8390ee69ca880ca17ccbb3f124
CRs-Fixed: 529272
Signed-off-by: Sameer Thalappil <sameert@codeaurora.org>