qcacmn: Add QDF cpu hotplug APIs

Currently, there are two consumers of the Linux kernel CPU hotplug APIs.
Besides being problematic for not being operating system agnostic,
different versions of the Linux kernel export different CPU hotplug
APIs. In order to consolidate the various abstractions for different
operating systems and API versions, create a CPU hotplug abstraction in
QDF.

Change-Id: Ib17c6e3ed3a87a90a82d909a6c493360cab27855
CRs-Fixed: 2132632