pmem: Add fmem call backs

Add callbacks for request/release region to be used with fmem.
These files can be referenced in any board file for use with
any pmem device.

Change-Id: I1a1791bbf8fc00d3e324600aedb5361aa899bc4f
Signed-off-by: Laura Abbott <lauraa@codeaurora.org>
pmem: add support for reusable pmem

Individual pmem devices can now be marked as reusable. The
memory will be reused through fmem.

Change-Id: Id71c2e0c42f093420c241771d7a2620ed2accfc4
Signed-off-by: Laura Abbott <lauraa@codeaurora.org>
pmem: Check for valid virtual address while flushing

Return invalid error if a NULL virtual address is
passed for pmem cache maintenance ioctl's

Change-Id: I18c369d4c2ac790b622408a988d171d6f75c4cd3
Signed-off-by: Shubhraprakash Das <sadas@codeaurora.org>