eglfs: Sanitize the X11 hooks

Replace all xlib calls with xcb equivalents, leaving only the
absolutely required xlib calls. Handle WM_DELETE_WINDOW so that
closing the window exits the app as expected. Finally, introduce
EGLFS_X11_FULLSCREEN to enable requesting a fullscreen native window.

Change-Id: I8c46ae832d38549ec7d673592f400a4f34bf4314
Reviewed-by: Andy Nichols <andy.nichols@digia.com>