Donot compose layers if external is in pause state

* Donot compose external/virtual layer-list when
when external/virtual is in pause state.
* Marking the layers for GPU composition when external/virtual
is in pause state would update FB_TARGET layer which inturn would
affect partial mdpcomp after resume.

Change-Id: Id2806bd7156085c00158a31dff3c3dc4c2b61146