mdss: display: add overlay ioctl apis to mdss driver

- Add support for overlay IOCTL APIs defined in linux/msm_mdp.h
- Support for ion client buffers and framebuffer memory

Change-Id: I0418ecab9aacf826d900f82f179fa20688fc763e
Signed-off-by: Adrian Salido-Moreno <adrianm@codeaurora.org>