egl: check if a window/pixmap is already used on surface creation

egl: check if a window/pixmap is already used on surface creation

The spec says we can't create another surface if we already created a
surface with the given window or pixmap. Implement this check.

This behavior is exercised by piglit/egl-create-surface.

Reviewed-by: Tapani Pälli <tapani.palli@intel.com>
Reviewed-by: Eric Engestrom <eric.engestrom@intel.com>
Signed-off-by: Paulo Zanoni <paulo.r.zanoni@intel.com>