wlan: Serialize OLPC mode before sending to FW

Currently the driver sends OLPC mode to the FW without serializing
which can cause out of sync issues with the firmware. Also the FW needs
to come out of power saving mode before processing this request.

Serialize the command and bring device out of power saving mode before
sending the command.

Change-Id: I6f0ee7cdef1f841c6ee3e1db2b92e9714cd25cb6
CRs-Fixed: 2699024