correct the zpos and capability of layers

correct the zpos and capability of layers

  If a TDM backend support PP, when video is playing, the display
  server normally will convert a video image with PP and show it
  to a GRAPHIC layer. If a GRAPHIC layer fully supports scaling,
  rotating and various color formats, the display server will show
  a video image to a GRAPHIC layer without converting.

  However, some hardware vendors want to handle a video image directly
  inside of their TDM backend module. If a TDM backend module offer
  VIDEO layers, the display server will pass a video image to the TDM
  backend module without any modification. No scaling, no rotating.
  And also, the display server won’t check video formats too. Then a
  TDM backend module has the responsibility to display a video image
  on the screen.

Change-Id: I932916f756291a40ddb8b19048d065769e8072e8