sf: virtual display clean up

  Since HAL allows Virtual devices, remove virtual display id
  check during setup of virtual display.

Change-Id: I6ec93c0f06842b69e6677f05ae8b45fb1f4225f6
libgui: Fix building with QCOM_BSP + CAF display

Change-Id: Iaf0eb69fa7f409144a266ada683fceb835f62aff
Forward-port surface dithering from CM10.1

This allows the use of 16-bit color displays without excessive color
banding;

Change-Id: Icb469b9cb4beb686516c60bb576dbd0a73f505e0