msm: mdss: restructure rotator code and add mutex for rotator api

The rotator data structure should be maintained in the rotator file
and rotator api calls should be following current ioctls, namely,
rotator_setup follows overlay_set, rotator_play follows overlay_play,
and rotator_unset follows overlay_unset. In this way, rotator code is
modulized and data is isolated easily by adding proper locking.

CRs-fixed: 563019
Change-Id: I3aa0db57d65cf9ae88c7e7cbccb3fa73a25e5902
Signed-off-by: Huaibin Yang <huaibiny@codeaurora.org>