msm: kgsl: Cleanup memdesc flags

We had a ugly mix of flags from usersapce mixed in with internal flags
and the flags were stored in priv and the internal flags were stored
in flags and general confusion all around.

So, external (user) flags moved to memdesc->flags, internal bits moved
to ->priv and now we are ready to handle the full onslaught of user
specified flags.

Change-Id: Ic0dedbad2236ae353b31e5dcaa6ff551713abaf1
Signed-off-by: Jordan Crouse <jcrouse@codeaurora.org>