Add support for split display

Configure LEFT and RIGHT mixer separately
Update split display
Fixup coding style in framebuffer_qcom_overlay.c
Kang qcomm overlay vsync and double-buffering from CM

* Largely inspired by
  https://github.com/CyanogenMod/android_bootable_recovery-cm/commit/3da7aae3125dbc682f0f3b3c468ca402e53ca5b1
* Fixes tearing on flo
Fix some typos in vsync code
Make qcom overlay vsync optional

* It is utterly broken on flo
Add device hook to allow incomplete fstab file

Conflicts:
	multirom.c