drm/msm/sde: add resource manager to enable dual dsi

Add resource manager for retrieving the control paths and layer
mixers. Encoder and CRTC use this to get the hw driver contexts
for those blocks.

Change-Id: Id6789ef24616197a295bcb5687a0de659cc11e5d
Signed-off-by: Abhijit Kulkarni <kabhijit@codeaurora.org>
Signed-off-by: Krishna Srinivas Kundurthi <kskund@codeaurora.org>