Adds initial support for VK_KHR_wayland_surface.

Adds initial support for VK_KHR_wayland_surface.

Very basic Wayland support is implemented by importing
memory with VK_EXT_image_drm_format_modifiers.
The current implementation requires an external system
memory allocator. An API for this allocator is defined
in util/wsialloc/wsialloc.h and an implementation using
the ION memory allocator is included.

Outstanding issues:
 * This is an initial prototype for Wayland support and
   has many outstanding TODOs which need addressing to
   properly use the Wayland protocol.
 * Using ICD Exported memory instead of a system allocator
   is not implemented.

Wayland support is still experimental and outstanding issues
will be fixed in future commits.

Change-Id: I1b0d5991e15ff1cf25ebbab3392a631b021e8c17
Signed-off-by: Rosen Zhelev <rosen.zhelev@arm.com>
Signed-off-by: Iason Paraskevopoulos <iason.paraskevopoulos@arm.com>