drm/msm: add multiple CRTC and overlay support

MDP5 currently support one single CRTC with its private pipe.
This change allows the configuration of multiple CRTCs with
the possibility to attach several public planes to these CRTCs.

Signed-off-by: Stephane Viau <sviau@codeaurora.org>
Signed-off-by: Rob Clark <robdclark@gmail.com>