Move WSI type specific calls

Move all WSI type specific calls to WSI factory methods. This
removes headless references in layer/ and allows for simpler
support of multiple windowing systems.

Change-Id: I757a7a3bb4267783420b52cceb3bde8ce233297e
Signed-off-by: Rosen Zhelev <rosen.zhelev@arm.com>
1 job for dev/staging_wl in 1 minute and 13 seconds
Status Job ID Name Coverage
  Test
passed #932095
build_vulkan_wsi_layer

00:01:13