Add vendor version for libgui

libstagefright_omx library need to be extended to vendor which
is depenednet on libgui which is a vndk_private lib.
Creating vendor version so that libstagefright_omx_ext can link
to libgui_vendor.

 Conflicts:
	libs/gui/Android.bp

CRs-Fixed: 2258968
Change-Id: I777eebffc405c8bb74aab270e9f272c806501458
Signed-off-by: Volodymyr Zhdanov <wight554@gmail.com>