hwc: synchronize PLL settings change API

 Protect the PLL change sequence when multiple clients
 try to change the PLL from different processes

Change-Id: I37691e275d871b2be4b926ba8433bcccd5d2ff0a
CRs-Fixed: 503309
hwc: Use correct z-order in video overlay

Set z-order of video layer to 0 and framebuffer to 1 in case
of video overlay composition so that the blending takes effect.

Change-Id: Ia700f88a8ebb8125a4424523cad1da5551e9b849
CRs-Fixed: 510241
Merge " hwc: synchronize PLL settings change API"
Merge "hwc: Use correct z-order in video overlay"