Add support for arbitrary number of layers

Add a static string in vulkan_layer_path that is set by the loader.
This path is then searched inside the loader for layers to load.

Change-Id: Ibd6fa87579d6fd39bba0814935be2bd38a416848
(cherry picked from commit 1dd0ae574084204bbbb614e551125ee84dc5cf3d)
1 file changed