wayland: Add support for the Wayland winsys

* Adds EGL_WL_bind_wayland_display extension
* Adds wayland-egl library
* Adds wl_dispmanx_buffer protocol extension

TODO: Check that platform_get_dimensions() returning swapchain_count == 1 is correct

TODO: Remove the requirement of passing a valid DispmanX element handle to
the SwapBuffers and CreateSurface RPC calls. This will remove the need to open
a DispmanX display from the clients.

TODO: wl_dispmanx_server_buffer should probably be defined in a
private header that can be included from EGL and vc_* instead of in
vc_vchi_dispmanx.h
wayland: Add Wayland example